It's been a while since I watched it, but do you think Ben Affleck's character in Good Will Hunting was rational, but of limited intelligence?

Yep, a pretty good example, I think

Look, you're my best friend so don't take this the wrong way, but if you're still living here in 20 years, still working construction, I'll fuckin' kill ya. Tomorrow, I'm gonna wake up and I'll be fifty, and I'll still be doing this shit. And that's alright, that's fine. But you're sitting on a winning lottery ticket and you're too scared to cash it in, and that's bullshit. Cause I'd do fucking anything to have what you got. Hanging around here is a waste of your time.

So far, so normal, you don't need to be a rationalist to say these sorts of things to make your friend start using their talents.

Every day, I come by your house, and I pick you up. We go out, have a few drinks, a few laughs, it's great. You know what the best part of my day is? It's for about ten seconds, from when I pull up at the curb to when I get to your door. Cause I think maybe I'll get up there and I'll knock on the door and you won't be there. No goodbye, no see-ya-later, no nothing. You just left.

Now this is what it looks like when a rationalist actually believes in something. You actively enjoy imagining your friend's left without a word, a horrible thing for a friend to do - because you knows that your friend starting to use their potential is so important as to drown out even being totally abandoned by them.

strong language