Its probably genetic. "The most common causes of intellectual disability include: Genetic conditions such as Down syndrome Problems during pregnancy that impact brain development such as drug and alcohol use Labor and delivery problems, such as not getting enough oxygen at birth Injuries such as head trauma and illnesses such as meningitis and seizure disorders" I could tell you what its like to be smart, but you probably wouldn't understand. On the other hand you're probably not as dumb as you think. What's your IQ? You most likely have an average IQ, 70% of the population does. If yours is lower its not your fault and the only thing you can do about it is learn as much as you can. Also there are many different kinds of smart. You may be challenged in one area and really smart in another. I've learned some very important lessons from my niece whose IQ is in the 40's. She's a real sweetheart! Being smart has its challenges, too. My son said being smart made him feel lonely. And its frustrating when you can't share your most brilliant ideas with anyone because no one else understands what you're talking about. Don't worry about what you're not. Just make the best of what God gave you and be thankful you are bright enough to post your thoughts on social media. My mentally retarded niece can't key her ideas because she only knows how to sight read about 100 words.

When your brain goes blank, it interrupts your ability to think. Being smart is to be on top of your game.

If any of you lack wisdom, let him ask of God, that giveth to all men liberally, and upbraideth not; and it shall be given him.

Everyone is dumb at something. Einstein was pretty dumb when it came to hygiene. He was so filthy at times that he was practically crawling with lice.

Just stop self-proclaiming yourself dumb and see the magic!

Check out the Dunning-Kruger Effect. It basically boils down to incompetent people overestimating their competence. Once you start catching on, people tend to over-correct and underestimate their abilities. So, by thinking you are dumb, you indicate that you are likely on a mental upswing.

You're not Dumb. Intelligent person who does stupid things is still stupid or dumb. You are what you do.