In scientific fields, luck is often described as occurring where chance and wisdom intersect. For example, Wilhelm Roentgen noticed that an experiment he was conducting on cathode ray tubes produced a glow in a nearby piece of equipment. This was an unintentional consequence of his experiment, but he was curious enough to investigate it and thereby discovered X-rays. Alexander Fleming returned to his lab from vacation and noticed that some of the bacteria he was growing appeared to be dying in the presence of mold that had accidentally entered a window; he pursued his observation and discovered penicillin. Richard Feynman noticed how plates in a college cafeteria moved at certain rates of spin and wobble. He pursued that insight and made a major contribution to quantum physics.

A fortunate happenstance can often be predicted. The chance of drawing a specific card from a deck has a mathematical likelihood that anyone can know. The possibility does not guarantee what the next card will be, but it makes the draw predictable. In contrast, superstition is an irrational belief, based not on empirical evidence, that the next card will be “lucky.” Feynman gives an example of the distinction when he talks with a professional gambler who tells him that he, the gambler, knows “the odds for all the numbers inside out” and knows that the odds are always, in the long run, in favor of the casino.