The obvious answer deserves extra scrutiny when the problem is complicated.

Simple problems have simple answers, and there the obvious one is usually right. Complicated ones are different: their obviousness often comes from having been simplified in your head before you looked. The first answer that arrives is shaped by familiarity, by what worked last time, by what would be easiest to explain. In a genuinely tangled situation, that ease is a warning, not a recommendation.

When a complex problem produces a fast clean answer, spend ten minutes trying to break it. Ask what would have to be true for it to work, and whether those things are actually true here. If it survives that, act on it with more confidence than before. If it does not, you have saved yourself an expensive month.