I wish I would've been as smart.

I would agree with you if overthinking would be caused by voices in the head that only you can hear, or extreme sensitivity to whatever happens around you.

However, overthinking is usually caused simply by a lack of discipline in thinking, and not knowing how to properly deal with certain things in life.

From your strong opinions, you seem to be (correct me if I'm wrong) the type of person who doesn't really get affected by many things in life, like what people say about you or not getting a job.

Others however have a harder time when it comes to those things. I personally knew people who spent hours overthinking a simple "no" coming from a random person.

I don't have that problem and I usually overthink when it comes to work more than anything, but it's still there, and what I need isn't a psychiatrist, but discipline.

It's kind of a broad subject that cannot be categorized as being a disease or not.

Just like the example with the class, you were smart enough to be capable of learning things in your own time and not pay attention to teachers that weren't teaching you anything useful.

Others however aren't like you, and actually pay attention to those teachers because they think it will help, or simply don't have what it takes to be responsible and learn in their own time, find their own information and learn more useful things.

I paid attention to teachers too until I realized what you did, the only difference being that it happened when I was 14, and even then, I wasn't smart enough to start learning things on my own.

If you categorize overthinking as a disease, because you don't experience it, I could also categorize you as ill if you cry or grief for losing someone in your family or close to you, just because you feel empathy, and I don't.