The same rule - it's temporary - applies just as well to Genius for most of us. There are complete idiots and there are complete geniuses, but most of us will bounce into both categories from time to time.

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