Sure, but that's trickier.

You can't see what's going on in their head, so it's really difficult to know whether you're actually correct or if you're missing something.

And, even if you are right, it's really tricky to know what you should do with that information. It's probably inadvisable to use it negatively against someone. And, even if you're trying to help, knowing what's wrong is very different than knowing how to effectively help someone fix the problem. Helping is an entirely different skillset than figuring out what's wrong.

So yes, it can be helpful, but analyze/diagnose other people with great caution and at your own peril.