What we do on some great occasion will probably depend on what we already are; and what we are will be the result of previous years of self-discipline.
The real sting of Liddon's observation lies in its reversal of how we usually think about character: we imagine ourselves capable of heroism *when the moment arrives*, but he suggests the moment merely *reveals* what we've already built. Notice he doesn't say "what we choose to do" but "what we already are"—the difference between intention and being. A surgeon's steady hand during an emergency procedure wasn't born in that operating room; it was forged through thousands of hours of unglamorous practice, repetition, and small decisions no one witnessed. This explains why people so often disappoint themselves in crucial moments—not from cowardice, but from the accumulated weight of years spent elsewhere.