It’s not true, they are not dumb, they are just being lazy.
I say lazy because this person does not understand what is being taught to them because they have decided that they don’t want to know. Maybe they are not interested in what they have to learn, maybe they are afraid of failing or it could be a thousand other reasons.
The main issue is, is that this person refuses to concentrate on what is going on, and they say time and time again that they can’t learn because they are dumb.
Saying that they are dumb is an excuse to get out of the work. They hope that they will be left to do their own devices.
So how do you get past this dumb defence? It’s not easy, but the one thing you cannot do is give in to it. You need to remain calm and focused and work with the person.
First you need to find out why they are not willing to learn what you are trying to teach. Maybe their bored, maybe they afraid of looking silly if they fail, or maybe they are just not interested in the subject. Whatever the reason you need to get past it with them.
The second thing you need to do is to make things interesting, break it into small steps and work with them. Encourage the person, praise them, and have a laugh at any mistakes. You will normally find that once the person has a few small successes in what they are doing will help to motivate them and you will be able to leave them alone to do their own learning.
Getting angry, yelling and telling them they are stupid will just work against you, they will pull back to their dumb defence and you will have lost them. Once you have lost somebody it takes an awful lot of work to get them back.
So when someone says that they are dumb, don’t get angry with them, see it as a challenge to motivate them and to help them learn. The best way for you to be motivated or learn new material is to help somebody else be motivated or learn new material.