I don't know what you do or don't understand, what you chose to understand or what you decided to ignore, because I don't know anything about your education, your childhood or anything about your background. You may have decided to be not be particularly smart about math, for example, or your parents weren't particularly smart and told you it was okay to hate math... but I do think that how smart you is based on a series of decisions you've made over the years about what you were good at. But stuff happens. Perhaps you suffered some degree of brain damage so to some extent it is out of your hands how intelligent you can be.
There are all kinds of ways you can do to improve your intelligence.
1. Always check your assumptions. It can take awhile to even figure out what your assumptions are. Keep hunting, there is so much gold in finding out what your assumptions are. But beware the journey into wonderland like: what is real, who am I... this is the stuff of philosophers..., so be warned!
2. Question your sources. They may be saying something you've heard before, but it doesn't make it true. Why are they saying it, do they benefit from me believing, repeating what they said/say? If someone is saying something different, is it necessarily wrong?
More can be found in Sagan's baloney detection (critical thinking) kit, something we need commonly and now more than ever.
I remember thinking government is the problem, I'd heard it said, and I believed it. I have no idea why I even thought it, but I decided my belief was based on no real research or science and there are a great many people who benefit from dis-empowering government. For example I get much more from govt than I get from business. For example a stable economy, government is currently trying to control corporate greed by slowing inflation.
People will always try to put you in a box. Once they figure out which box you belong in, you are easily dismissed as irrelevant. The only way you can avoid being put into a box is by not using your most powerful weapon, your brain.