Inner Critic
IC: You did so bad in the class because you are not good enough in math.
IG: Maybe I am not good enough in math, I can make up by working hard.
IC: You did so bad because you have no idea about how to prepare for tests.
IG: I did not know how to prepare for the test indeed, but I can learn to do it and nail it.
IC: You did badly in the test because you are stupid.
IG: I might be stupid in math, but I must be smart in some other subjects.
Inner Defender
ID: You failed the test because your classmates are much better than you.
IG: Although I did worse than them in the test, they are also humans, I can still catch up by studying hard.
ID: You failed because the instructor did not make his points clear.
IG: If I think the instructor did not make it clear, go and ask him.
ID: You failed because there are too many problems in the test.
IG: I failed to finish the exam, so I need to practice doing math problem quicker.
Changing my inner conversation helps me to find out that there is no problem cannot be solved and no excuse to not do well in class.
The only way to get good grades is to study hard instead of finding pretexts.