That's because of quantum effects. Position and Momentum are the best known examples of the uncertainty principle, but others exist, such as doppler and range, or time and dryness - that last one being known as the Paint Pair and states that the more you know about how long it has been since nails were painted, the less you know about how dry they are.
That's why nails dry best when you dissociate listening to a book or watching a TV show, because you lose track of time. Then all of a sudden you go "it's been awhile, how long have I been doing this? I bet the nails are dry by now" and it's always true but if you go "it's been like fifteen minutes, I bet the nails are dry by now" you're very likely to encounter wet nails.
If I'm in the locker, that means you know I am not moving. Since my momentum is certain, my position is not. I am no longer in the locker.