I hate it when things don't work even when you try. Why the hell does that experiment have to quit with an error 15 minutes before the demo? You work furiously all night on making the damn thing work, from scratch, when it could have been easier to modify an existing one. Just because you believe it's going to be better in the long run. And it does work. Very well, albeit with a few rough edges. You're happy and cheerfully declare that you are going to go ahead with the demo. Except that the demo does not want to go ahead. Along with itself, it takes away all your credibility.
I hate life.