So for example I was always told that I was very clever all throughout primary school. I was constantly praised by teachers and my parents for being brainy. In fact I was probably just a good reader and a bit more ahead than some of the other kids, but I've carried this belief. I've got zero evidence of being clever as an adult but I was told so much the belief has never gone away.
Otoh I was also constantly told I was shy, nervous and not very good at sport and I have carried this belief too and always been afraid of trying things.
Dh was always told that he was slow and a.bit stupid and again, even though he's done very well he always puts himself down about being 'thick'.