The point isn't how you feel *during* the exam, it's how you feel *after*. Yes, of course most people are going to feel anxious when they notice that they've selected 'C' for every single answer, and are going to doubt themselves. But it can give an important lesson when the exam comes back and it is revealed that those were, in fact, the correct answers. It gives you a prompt to reflect on why you felt so anxious about the answers being the same, and if you changed some of the answers just to avoid having all Cs you might think, "I really should have just been confident in my knowledge, because I had the right answers in the first place."