A thought repeated long enough eventually starts introducing itself as truth.

Repetition is how the mind decides what counts as background fact. A sentence you say about yourself a few hundred times stops being reviewed and starts being assumed, the way you no longer check whether the floor will hold you. The danger is that the sentence never had to be true to earn that status. It only had to be frequent.

Listen for the lines you say about yourself automatically, especially the ones that begin with I always or I never. Write one down exactly as it sounds in your head, then look for the evidence you would need to convict yourself of it in a fair hearing. Most of these sentences survive on repetition alone, and they get quieter the moment you make them prove themselves.