Teachers are fallible. They make mistakes. Sometimes they simplify or, worse, over-simplify.
They don't even produce perfectly deterministic responses; give them the same question twice, and you might get two slightly different explanations. Hardly a thing you'd want to rely on for something as important as learning.
Sometimes they guide you toward conclusions others already agree with. If you let a teacher instruct you, how can you be sure the thoughts are truly your own? Better to avoid all of that and instead rediscover established knowledge independently, one inefficient breakthrough at a time.
There are social effects, too. When you learn something from a teacher, what are you really demonstrating? That you can absorb information presented clearly? That you can benefit from accumulated knowledge? Where is the credibility in that?
No. If you want to build trust, you must struggle visibly. You must arrive late, battered, and slightly incorrect, but undeniably self-derived. Only then can others be confident that the thinking, however flawed, was authentically yours.