Be careful. So will the less-than-best essays and teachers. It's a form of hindsight bias: you think this thing is obvious, but your thoughts were actually quite inchoate before that.

Given a clear explanation, it's more probably correct than secretly wrong. We don't live in a world dominated by true-sounding lies. Incorrect things should be generally more surprising than correct things, even if there are exceptions.

(It's confirmation bias, not hindsight bias. Hindsight bias is overestimation of prior probability upon observing a positive instance of an event.)