I don't consider moving stops, impulsive entries, deviating from plan, etc. to be errors, but bad decisions.
I seem to make 1-2 bad decisions per month.
-After a slow period, I'm tempted to take an impulsive (non valid) entry that "looks good".
-After a losing streak, I'm tempted to look for a bigger target than what my trading plan is designed to capture.
The immediate result is "extra profits" or "extra losses". My long-term result has been negative.
IMO, the biggest problem with bad decisions, is that more follow.
If you take a non valid trade, move your stop, etc., and you make "extra profit", you're likely to repeat the action in the future.
If it goes bad, you'll lose money that you shouldn't have lost, and then probably start looking for another "good lookin'" entry (that isn't in your plan), as you try to get back to even.
The bad decisions are gambling. If you have a tested plan that is working, just press the button when you get a signal, exit where you're supposed to, and live with the results.
If you don't like your results, analyze and adjust.
DON'T TRY TO OUT TRADE YOUR PLAN.