I believed that for years, I did CBT, changing beliefs, "just do it" et cetera and I was helpless still, went from one addiction to another. Turns out I had ADHD. My life was totally changed after medication.

You don't have infinite willpower. If humans had infinite willpower humanity would have worked itself to death long ago. There is a natural balance of willpower in your brain, it's called the dopaminergic system. If you have ADHD, you have much, much less willpower than a normal person because you literally lack the dopamine hormone in your prefrontal cortex. No amount of belief will magically create dopamine in your brain out of thin air.