Psyblog has a rundown of 18 failures of the brain’s system of attention.  My favorite:

9. Ironic processes of control

In fact sometimes attention is a real bear. What about when you really want to get something right, like putt the ball, hit a beautiful serve right in the corner or reverse the car into a narrow space? Naturally you concentrate even harder than normal, really focus. Unfortunately that just seems to make things worse: you miss the putt by a mile, frame the ball 50ft in the air and ding the car. What gives? These are what Wegner et al. (1998) call ‘ironic processes of control’. Sometimes too much attention is just as detrimental as too little.

I normaly strive to pay as little attention as possible.