Look at the last three times you blamed a teacher. Was there anything in common besides the teacher?

Any single bad class can genuinely be the teacher. Three in a row starts to describe something that travels with you, whether that is boredom, being corrected, or a subject you quietly gave up on early. Looking for the common thread is not the same as deciding it is all your fault. It is just the only part of the pattern you can reach.

Write the three down and look for what repeats: the time of day, the subject, the moment things turned. Pick the smallest repeating thing and change it once this week. If nothing repeats, you have your answer and can stop carrying the question around.