It's idle to debate whether a step is "simple" or not; for some it will be for some not, depending on various factors.
Once a problem is solved and the proof is tested it's quite easy to say "Aw, yes, all but simple steps." - now, getting to this solution is a completely different thing.
Let's just take a slightly more difficult problem -
Euclids Proof of the infiniteness of prime numbers. It's very easy to grasp .. but I'm quite interested if anyone's willing to argue that it's easy to come about it.