Character […] isn’t a stable, easily identifiable set of closely related traits […]. Character is more like a bundle of habits and tendencies and interests, loosely bound together and dependent, at certain times, on circumstance and context. The reason that most of us seem to have a consistent character is that most of us are really good at controlling our environment. (emphasis added; page 163, pbk ed)
Gladwell’s comment pertains to real-people personality traits, but it also speaks to characterization in the writerly sense. Writers are advised to let characters develop beyond simple cliches, into surprising, conflicting, complex people. We’re advised to let more, and worse, things go wrong for them. Aha, I get it: it’s precisely when things begin to go wrong -- when characters lose control of their environments -- that they begin to reveal their complex selves.