I recently failed to pass a first round interview at a top consulting firm. The cases felt very easy and straight forward. The HR feedback focused on minor mistakes that I never thought would be a break dealer ex: "you didn't need to ask to convert cm to m, didn't need to ask calculation confirmation, etc." I've passed cases before that went a lot less smooth than this one (although in a smaller firm).
I'm wondering if sometimes interviewers will find small mistakes to use as an excuse to not pass a candidate because of other, harder to explain reasons (maybe they simply didn't like my personality. In hindsight I might of been cocky given the relatively easy case). Or should I really aim for perfection in case studies?