Everyone's an idiot some of the time (Scott Adams anecdote)
blog.brianguthrie.com
blog.brianguthrie.com
There's an excellent TED talk from Elizabeth Gilbert [1] on the history of 'genius', which originated as a term to describe someone being supported by a genius, not that they were intrinsically a genius themselves and at all times.
Worth considering next time you completely stuff up; and probably even more valuable to consider next time you nail something perfectly, and believe it will continue.
[1] http://www.ted.com/talks/elizabeth_gilbert_on_genius.html
Idiocy is also not synonymous with ignorance or foolishness.
"An idiot differs from a fool (who is unwise) and an ignoramus (who is uneducated/an ignorant), neither of which refer to someone with low intelligence."
http://en.m.wikipedia.org/wiki/Fundamental_attribution_error