In this case, the result seemed odd, so I checked it by stepping away from the spreadsheets and FEM software, and simplifying the problem down to a quick hand calc. But if I hadn’t done this exact exercise on dozens of buildings, I might not know what ‘odd’ looks like.

Luckily, in this field, you can usually come up with a quick check that gets you within +/- 20% of the more sophisticated answer. These kind of sanity checks should be baked into the design process, but unfortunately not everyone seems to do them.