This is the lie that keeps people addicted. Plenty of people quit their very real addictions every day. If you imagine you're helplessly addicted, you will remain addicted.
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.