Is it normal to sabatoge my efforts?

I'm not sure if I'm doing this subconsciously or consciously but sometimes when I am taking awesome strides to achieve a goal, I sabotage it somehow - sometimes right before the payoff. The worst part is that I know what I should be doing and what I shouldn't be doing; I know what I logically need to do. I assume it has to do with emotions, I just hate emotional decisions where they don’t belong.
Does anyone else do this? I would love examples.