The boulder was not resting on a flat surface that a lever could be applied beneath. It was a chockstone — wedged between two walls of sandstone, with contact points distributed along its surface wherever stone met stone. The friction at those contact points, multiplied by the boulder’s weight and the geometry of its position, created a resistance to lateral force that was very different from what it would take to simply lift the same boulder off a flat surface. A chockstone in a narrowing slot can be held in place by friction forces that are a multiple of its weight — the greater the narrowing, and the more the walls have worn into the stone, the greater the friction coefficient that must be overcome.
Ralston had a climbing rope and, presumably, a small selection of hardware appropriate for technical canyoneering. The anchor systems he could construct in the available space — anchors that had to be placed in a three-foot-wide canyon with sandstone walls of limited texture — were limited in their mechanical advantage and in the magnitude of force they could safely apply. Even a Z-pulley system, which is the standard backcountry method for creating mechanical advantage with a single rope, multiplies force by a factor of three. Three times his own pulling force was not, against an 800-pound chockstone wedged in a narrowing slot, a decisive improvement.
The Outside magazine account notes that after rigging his ropes and applying what force he could, the boulder “didn’t move, not even microscopically.” This is not a rhetorical flourish. In a situation where any movement of the boulder, however small, might create an opportunity — a change in the pressure on his arm, a shift in the geometry of entrapment that opened some alternative — even microscopic movement would have been meaningful. The boulder provided none.