Myth: Lightning never strikes the same spot twice
File this one under "things you know that just aren't so," right next to "humans only use 10% of their brains" and "science says bumblebees can't fly:"
Lightning never strikes the same place twice.
The fact is, lightning doesn't have a memory. Thunderheads don't keep a record of where they've sent lightning bolts before, and in many cases storm systems may preferentially hit the same spot again and again. The Empire State Building is hit about twenty-five times a year, on average.
Now, granted, the Empire State Building is a special case. It's a tall, grounded structure with a lightning rod on the top, so as far as lightning's concerned, it's the Promised Land.
And speaking of lightning rods, most people know that the lightning rod was invented by Benjamin Franklin, but what's less well-known is that it quickly became a matter of political dispute between King George III and the Republic during the Revolutionary War.
Franklin's original lightning rod design, an example of which is shown here, called for a sharpened iron rod, mounted to the top of a building and connected by a copper cable to the ground. Franklin reasoned that a sharpened lightning rod would more effectively attract a lightning bolt, because it would more efficiently concentrate electrostatic charge at its tip. (This particular lightning rod is one of his originals; it's bent because of a lightning strike, which softened the metal and melted the tip.)
King George III favored designs with rounded balls on the top, in part because Franklin was one of the signers of the Declaration of Independence. In 1776, a powder magazine in London was struck by lightning and burned; the Franklin lightning rod protecting it was quickly blamed, and lightning rods with rounded ends were soon mandated by law in England.
As it turns out, ol' King George was actually right, and modern lightning rods in the US have a rounded top. Lightning doesn't work the way most people think it does. When a lightning stroke travels from a cloud toward the ground, it's met by a riser, or "streamer," that rises from the ground to meet the incoming stroke.
A lightning rod does not prevent lightning from occurring. Instead, a lightning rod provides a convenient focal point for the streamer; the idea is that the lightning stroke will preferentially hit the lightning rod, rather than hitting, say, the top of the house, or the car parked out front, or the neighbor's cat. (Lightning does not always strike the highest point in the area; instead, it strikes the point of highest charge density, where the streamer forms most readily.)
Charge density increases dramatically around a pointed object, so a pointed lightning rod is most effective at initiating a streamer. However, charge density remains uniformly high around a smooth surface, so a lightning rod with a rounded top is more effective at sustaining the streamer for long enough to attract the downward stroke. For this reason, most modern lightning rods, at least in the United States, have rounded ends, not pointed ends. (Some lightning rods try to get the best of both worlds by using a metallic tuft on the end, with lots of sharp bits to create high field potential and a large surface area to help support the riser.)
In any event, lightning can and does hit the same place twice. The only thing a lightning stroke cares about is the field potential of the area where it hits, and an area that's appealing enough for lightning to strike once will often be struck again. In fact, you can even predict the number of times lightning will strike in a given area, based on the part of the country you're in.