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.
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:
To me, this is why things like user personas are so important. You’re never going to get a design perfect, so you need to work hard to get it as close to perfect as you can (and keep adjusting to make it “more perfect” over time).
As Michael (Ted Danson) said once in the show “The Good Place”, anything can be up to 104% perfect. While that was just a funny line, it’s a good target and a reminder to keep iterating and improving as time goes on. Users will still find unique ways to break your interface, but the more perfect you can make it, the better.