People aren’t tennis balls

For an official Type 2 tennis ball, which weighs between 1.975–2.095 ounces, dropping it from a height of 100 inches should bounce back up between 53–58 inches. If you take the same tennis ball and do the same test, you’re going to get the same result.

People are quite different than that, which makes human-focused design very difficult.

On a recent episode of Guy Kawasaki’s “Remarkable People” podcast, he had Don Norman (author of “ The Design of Everyday Things “, among others) on the show. The entire episode was fantastic, but my thoughts on this post come from something Don said on the show.

He said:

And the physical sciences, look if I pick up something and I drop it, and I pick it up again, and I drop it, the fact that I dropped it once before doesn’t change the way it falls a second time.

That’s called path independence. People don’t have that. Whatever I do to you affects what’s going to happen the next instant. And that’s what makes it so hard to design. In fact, I once argued that you can’t ever make the perfect design because if you made the perfect design, people would use it in ways you’d never thought of. And then in those new ways, it wouldn’t be perfect anymore.

There have been thousands (millions?) of examples of this over years, summarized in fun pieces like this: