You make a mistake. Shit happens, nobody is perfect. Maybe your boss or client tells you that it is okay, just be careful next time.
Next time is right on the corner, and behold, you make another mistake... Things are told to you a little less nicely. You are doing your best, but you just keep making stupid mistakes. Mistakes you know you shouldn't be doing, but with the pressure, the stress, the rush... everything you do seems to be a major struggle.
I'm currently in this situation. I just can't seem to do anything right. I feel like I'm doing my best, but I just can't stop myself from fucking things up. People are losing money, or their patience, or their heads. I'm being quite pragmatic about it, as periods like that most likely happen to everyone.
Have you ever been in such a situation? Where you just have one of those days or weeks of being a terrible programmer? How do you deal with it?