Similar situations occur all the time. When you're in a hurry to open the door and you try several keys on the key ring , the last remaining key is usually the one that works. When you get in a line at the supermarket, you find you've chosen the slowest one, and it just doesn't move. Is this bad luck or coincidence? According to British physicist Robert Mathews, it's neither one nor the other. He explains that our Selective memories tend to remember the bad episodes more readily than the things that usually work out. Also, the law of probability is more against us than in our favor in many situations. For example, in the supermarket with five cashiers, the chances of getting the fastest lane are 20 percent, and 80 percent for a slower lane.