For the past year I've been noticing an interesting phenomenon, the "Why can't I do that on purpose?"-effect. This usually happens when I'm just walking by my computer desk or other piece of furniture, and throw whatever object I'm holding on it, in this case, a balled up bit of tin-foil from a piece of chocolate. The ball bounces off an emptied drumstick of chicken, instead of landing on the glass desk immediately.
Fascinated, I try and hit the chicken drumstick again with the balled tin-foil, without success.
"How the hell did I do that by accident?"
There are actually a number of different things on my desk that the balled up bit of tin-foil could have hit to elicit that same reaction from me; the plastic candy wrappers around the chicken drumstick, the fork next to it, anything. However, if I try to hit the chicken drumstick, my reaction to the balled up tin-foil hitting the candy wrapper instead will be "Why didn't I hit the chicken wing?"
In other words, suppose there's a 50% of eliciting reaction A, due to there being 5 objects, for each of which there is a 10% chance of hitting them. If I hit one of them and elicit reaction A, I decrease the probability of re-eliciting reaction A to 10%, because the other 4 objects, if hit, will be disregarded.