That's the wrong way of framing it and it also depends on how you define dumb, and that's quite alarming if you're going to become a psychologist.
If we're talking about cognitive ability, there are people who are dumb in that sense because they have an IQ of 80, and not matter how much they try to educate themselves, they won't become smarter. They will never be able to read instructions and follow them for example. IQ is pretty much static so they'll always be stuck at that point no matter how hard they try.
You can also have an IQ of 130 and fail to educate yourself properly. But that person will still have the potential to turn things around and to become smarter. And since one way to define IQ is the speed at which you can process complex cognitive tasks, they'll be able to catch up quite quickly.
Where you land on the IQ distribution is largely determined by your genetics (or nature):
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Now if you don't believe in IQ, God help your future patients.
Where did you get that I don't "believe" in IQ. LOL
Halucinations?
We all know what is IQ, hunny. You talked in derogatory sense of dumb and smart, not in the measurable genetic sense. And majority of people are average in intelligence, meaning they are pretty much equiped to be educated.
Alos GOD, is that food? What is that?