I can assure you that any roped free climber, regardless of experience or ability, on a serious and committing friction lead has known the fear to which my title refers. This subject comes to mind in the wake of Daniel Duane’s recent brilliant piece in the New York Times  on Alex Honnold’s free solo ascent of Freerider on El Cap. In it are evocations of the primal fear of having to trust the shoes while the hands are essentially useless, and of the fatal urge to lean in toward the false comfort of the cliff face.
A climber can easily sense any small increase in steepness which might lead to a slide:
“It still felt really insecure and I still always felt like the feet might slip,” [Honnold] said …
According to the Web the coefficient of friction of a climbing shoe sole in contact with various rock surfaces varies from 0.9 to 1.1 and is often higher if the surface is particularly rough. For my purpose here I will use a coefficient value of one.
This means, for example, that a shoe vertically loaded on a featureless forty-five degree slope has a friction resistance just balancing its tendency to slide. In this case there is no margin for error and to lean in from the vertical, however little, without foot slippage is virtually impossible. Slopes steeper than this are theoretically unclimbable by stepping-up alone, although there are steeper ones (on the Big Stone and elsewhere) with unusual roughness, or that yield to dynamic techniques, or to raw courage.
Desperate dynamic moments entail stepping up faster than the feet slide down, but have no place in controlled free soloing. Nor are we considering slopes with tiny ledges, or scoops, or places where the hands can do anything other than lightly kiss or even leave the face. Even roped, the friction leader has scant opportunity to set protection owing to a general featurelessness of slabs.
More commonly one is on a lesser slope, say of thirty degrees, as is typical of our own White Horse Ledge in New Hampshire. Here the geometry is more forgiving although it takes real conviction to be convinced of it. In this case one need lean in from the vertical only fifteen degrees for the feet to give way.
Amazingly Alex learned to control the fierce reluctance to stand free, in effect, putting his hands in his pockets and tip-toeing to the next haven a dozen steps above.
Two-thousand feet above the Yosemite Valley floor!
Although Cannon Cliff had been pretty well tamed by then, forty-some years ago, we Boston folk still viewed its distant 1,000 foot face with some measure of mystery, and respect. Indeed, Cannon was not without a reputation for danger. In 1968 a Dartmouth climber had been killed as a result of rock fall, and earlier two inexperienced boys had famously died of exposure—benighted on the cliff.
We ventured north maybe once a year—often later in the season; the wisdom being that the icy stresses of the previous winter had to be given time to relax.
Aside from some classic route descriptions published in Appalachia  before the War, Bob Hall’s detailed typewritten pages of 1967 were then the only available guide.
After one had climbed some of the reasonable routes like Lakeview, Wiessner’s, Old Cannon, and Cannonade, and had savored the airy exposure of the Whitney-Gilman, it was time to venture into more challenging territory. We looked to Sam’s Swan Song  as the next serious climb to do.
And so, in the early seventies, Tom Hayden and I went up to give Sam’s a try. We switched leads. The first pitch fell to me, next the short hand traverse on the third, and the long rising traverse right on the fifth. Tom led to the “Cow Pasture,” and I gingerly ascended a notorious rotten section above that ending below a steep jam crack. Tom led the crack—it was hard. I’m sure I yelled for “tension”; at the top my fingers cramped into useless hooks refusing to straighten. That eighth pitch seemed to have been the crux and we negotiated the final three or four to the top with no trouble. Great climb! At the top was a screw-top glass jar containing a register and a stubby pencil. In the very bottom was a scrap of paper closed with a clip enfolding a small joint . Its note read “To get a little higher.” Sadly, we had no matches.
A year or so later I went up on Sam’s again, this time with my friend Townsend Barker. The idea was that in swinging leads I would get to lead the pitches I had followed with Tom. And so it went to top of the rotten seventh pitch. I had just reached Townsend and tied in when, with a clap of thunder, the darkening skies opened loosing a torrent of cold rain which soon became hail—bouncing down the cliff and filling the cracks in the rock with little white marbles. The weather on Cannon comes in from the blind side. Soon we were soaked and shivering. To keep spirits up Townsend filled the moments with a long, inane shaggy-dog story at the end of which, and without much thought, we agreed that we’d best go down.
Townsend had a brand new, three-hundred foot bicolor rope. Two rappels, the second from the Cow Pasture, got us to the top of the rising traverse. We tied in to fixed pins and Townsend began pulling the recovery. In the middle of its “slither” phase the rope suddenly stopped coming. He pulled. Nothing. He pulled harder. Nothing. We pulled together to no avail. Townsend reached into his pocket and pulled something out—his knife. “Wait!” I said. “Let’s try one more time.” Against being unbalanced if the rope came suddenly free we tied into everything in sight. And we PULLED! Sproing! It gave way and a shoe-box sized rock hurtled, whispering softly by us to disappear crashing and banging below. As Town coiled the rope for the next throw I happened to look back out over the valley. “Town! Look!” And there below us was our reward—a magnificent double rainbow silhouetted against the green dark of the valley trees.
What next? The prospect of rappelling more or less sideways down the rising traverse was not appealing as, at forty-five degrees, it would have been hard to resist a strong side pull. Maybe we could have down-climbed it on belay somehow protecting against swings; and perhaps we should have.
Straight down the face was blank as far as we could see but there was a hint of a stopping place a long way down. I made sure I had the means to re-climb and started off. I went a long way, walking from side to side, and by the time I could see the rope ends I became concerned. Nothing was in sight. But, a little farther, a little farther, and—relief—there was a small ledge with a corner that would take protection. Only a foot or so of rope remained.
The protection there was good and two or three more rappels got us safely down to the top of the talus below.
Again, in 1976, I found myself up on Sam’s, this time as two ropes of two. It was our combined New York and Boston AMC Labor Day weekend trip. I had the lead rope seconded by a young woman whose brother led the second.
The climb went well and in pretty good time we reached the bottom of the penultimate pitch beyond which was one of class four scramble. And then (damn!)—it began to pour. There was wind and the rain was freezing cold. The squall passed fairly quickly but those without rain-wear got wet. I turned my attention to the next pitch which is steep and somewhat featureless, and has the unfortunate characteristic of offering hand and footholds that are largely upside down. The pitch was running wet. I traversed left and right seeking a way to get started and eventually concluded that I wasn’t up for it—not a good mindset for a leader.
The second rope declined to take the lead and we made the decision, probably too hastily, to go down. It was late. We might better have waited the hour or so needed for the pitch to dry. The young woman was shivering. Before starting the climb we had failed to do a thorough check on personal equipment and the result was that I was the only one with a headlamp. We realized then that we would be overtaken by darkness.
At dusk I reached the top of the rising traverse but the others had to set up and descend to me without a light in the pitch dark; a testament to the skill of climbers who know what they are doing.
And so here I was, yet again, at this spot facing a rappel into the void, but this time at least knowing pretty well that it was possible. The one problem might be if our ropes were not as long as half of Townsend’s 300-foot bi-color. If we had cut the rope that day I would never have known about the crucial ledge. And so, again making sure that I could re-climb if I had to, I started down in the dark. The headlamp beam (four D-cells) was pretty strong but faded out almost completely only eight or ten feet away, the ropes below vanishing into gloom. I went slowly, again walking from side to side peering down and sincerely hoping that what I had remembered was right.
Eventually I could discern the knots in the rope ends, but where were the ledge and crack? The knots were so close it seemed impossible that they would not be in sight. I paid out another couple of feet; end-knots now only a few feet away. Will I still be able to reach them when my weight is off? I think maybe to walk a bit farther to the right—and, suddenly, there it was! I had to stretch down to get my footing. There was not room for four here so one had to rap the next pitch before the others could begin their descent. It was slow going; we left gear behind.
Across the valley below there were lights at Boise Rock , among them police red and blue flashers. A distant bull-horn burst into stentorian sound echoing off the cliff and the distant peaks.
Not knowing whether to turn the lamp off for a bit and back on twice in succession, or to leave it on and turn it off twice, we blinked it more or less randomly and continued on.
We were met at the bottom around midnight by a New York AMC welcoming party who had delayed their long drive to New York to struggle in the dark for the hour it takes to climb the talus to bring us hot coffee and lights.
In July of 1981 I went with my Australian dear friend and climbing partner Ian Armstrong to the Tetons for two weeks. We warmed up on Baxter’s Pinnacle the first day, and then went up to do a two or three-day ascent of the East Snowfields route on Owen. Unaccountably I had new and surprising difficulty on this climb; Ian had to carry my pack most of the way to our first bivouac, and we failed on the route the next day because I was so slow on the ascent and totally exhausted by our retreat from the base of the East Prong, our highest point.
We thought it was lack of proper altitude acclimatization, but on a subsequent “test” backpack to the summit of Table Mountain again I had excruciating difficulty on the descent. I booked an early flight home leaving Ian to finish out his two weeks with Eric Engberg, Larry LaForge, and Bev Boynton.
In August Ian had returned and we agreed to go up on Sam’s. We swung leads. Above the Cow Pasture I remember grabbing the bottom-most of a stack of dinner plates which teetered ominously but did not fall. The climbing seemed easy enough; perhaps my problem was the altitude after all.
However, scrambling down the Whitney-Gilman walk-off couloir was something else—and it certainly wasn’t the altitude. I could hardly take a downward step; lowering my weight on the quadriceps was painfully tiring. It must have taken me more than three hours to make it from top to bottom.
A week later I learned from my physician that I suffered from Graves’ Disease, an excess thyroid imbalance leading to hyper-metabolism and a gradual wasting of the body’s large muscles. Fortunately there was medication to correct it and I spent the winter in the gym to regain my former strength.