What the mind tells me repeatedly
When I was young, I was labelled as "dumb" by my maths teacher. That stigma sticks with me dearly, even till now! I think that is a very common childhood nightmare, especially for the older generations.
So in a way, when someone told you that you are "dumb" back when you were a little kid, your mind started to record that "FACT", and every time you remembered that incident your mind records that exact same "FACT" again. And when you made a mistake and forgot something at home, or when you missed an appointment, or any of the things that made you call yourself "dumb" - your mind just proceeded to record that fact again.
So there's actually a vicious invisible cycle of bad affirmation going on in our subconscious. From here, constant repetition on that "fact" to your mind, has ingrained a belief in it that you are in fact "dumb".
Yes it sucks. It makes me feel less confident throughout the growing years as this little voice inside keeps saying I'm not clever. And sadly I believed in that and even when I tried to fight back, I did not know how. That's the living tragedy facing many people.