I know that negative thoughts are self-destructive

Having them is not the damage. Everyone does, hourly, including the people who look most assembled from the outside.

The damage is in the agreeing. A thought passes through and, instead of arriving and leaving, it gets nodded at. Yes, that is right, that is what I am. Each nod makes the next one arrive faster and stay longer.

Nothing in that makes you weak or badly made. It is repetition doing what repetition does.

Which means the work is smaller than it sounds. Not stopping the thoughts, which is not on offer to anybody. Just withholding the nod once or twice a day.