[a1a]

Schneier's Law comes to mind

"Anyone, from the most clueless amateur to the best cryptographer, can create an algorithm that he himself can't break."

https://www.schneier.com/blog/archives/2011/04/schneiers_law...

[kleer001]

Oh, that's what that is!

I had found a similar thing making my own puzzles, "It's easy to make a puzzle you can't solve, but it's hard to make a puzzle that's fun."

Well, that' not entirely the same thing, but they overlap I guess.

[lectrick]

It seems related to Dunning-Kruger

http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

[derefr]

I would compare it to a writer's inability to spot typos in something they wrote themselves. Probably, if the same algorithm was written by someone else, they could tear it apart easily.