The hard part about teaching is recognizing when you've introduced a large leap for a good percentage of the class.

There's a famous math story that goes:

"A professor was at the chalkboard writing up a proof for his class. At one point he comes to a portion of the proof and says, 'And it's obvious this must be X'. At which point he pauses, the class waiting. Stares at the board for a minute. Then leaves the class without saying a word. He returns fifteen minutes later, continuing, 'Yes, it's obvious this must be X'."