If you see a software engineer who is awfully giddy and grinning from ear to ear and you don't know why he or she is happy it's most likely the engineer just deployed code that works brilliantly.
It's not possible for a software engineer to leave unfinished work at the office because the mind of a software engineer is a virtual office that can't be stepped out of. When code isn't running or when bugs can't seem to be properly debugged a lot of software engineers have trouble sleeping or concentrating on other things as the mind keeps permutating and simulating different possible solutions.
A lot of times, bugs can arise as a result of the dev complicating simple tasks with overengineering which is when the dev decides to put in too many features than is needed.