That's fair - I have a coworker whose ears are shaped weirdly and he cannot use AirPods at all (or even the previous wired EarPods, for that matter)

It's a one-size-fits-all design and if it's a little off you're kinda out of luck. They fit me perfectly though which is one of the things that blew my mind initially. I didn't realize how many of previous fit issues were a result of having a cord that tugs when you make any movements.

I don't know if Apple changed the shape for AirPods (they look very similar to the EarPods) but the AirPods stay in my ears so much better, it's night and day. I've been attributing it to the weight/tug of the cable.