I worked for a major investment bank on their securities and convertible bonds trading software (think, evil mortgage backed securities). A typo could cause the DOW to drop and the global economy to go with it (it happened because of a glitch at another bank, a year or so ago, and my mother called to ask me if it was me ). Stressful as hell job, and you don't want somebody with poor judgement there. I screwed up a few times, luckily it was only in the test environment - which I once totally broke and ended up giving a bunch of people the rest of the day off because they had nothing to do till it was fixed.