It’s nothing to do with how smart you or anyone else is, and all about challenging your self and not getting stagnant.
You can be the least smart person on a project, but if it’s something you can do in your sleep, you will be bored out of your mind. Or you can be the smartest person, and if it’s a hard problem— whether that’s because it’s hard, or just lots of new things to learn— you will find it interesting.
Or at least, that’s how I find it works. It’s probably not universally that way.

