The last dumbest thing that I made was occasional deleting of my Bountyhive profile. My signature campaign was going to finish, I have participated in it during last 2 months, but at last removed all my work! Perhaps it is not such a hard case in comparison with the others, but I expected a good income from it, worked for two months and at last destroyed it just in one minute.
Also I have to say that reading about someone else's mistakes helps to be more attentive, so this theme is very useful)