@danluu this seems to track solidly with how alex honnold approaches his free soloing:
there usually is a very lengthy preparation period in which he repeats the route on some form of protection, to know exact solutions to every move that can get dicey. it’s naturally still not a guarantee, but a way to reduce as many controllable factors as possible to lower the risk on an activity with such high consequence.
during a live-tweeting of free solo (the film), he said that after he bailed on his first attempt on the freeblast slab, a climbing pitch where you rely almost entirely on very exact foot placements and if one foot pops, there are no handholds good enough to allow you to hold your bodyweight, he drilled it so hard that he could climb it free-handedly. he said he would’ve loved to see that in the film as an illustration of the amount of obsessive prep that culminates in climbing all of el capitan without ropes.
and even with that entire apparatus around the process, you can still hear him comment other peoples’ free soloing feats with statements like ‘you soloed what, for how many times? that’s completely outrageous.’ – some routes are just too spicy for the consequences, let alone repeating them.