I marveled at my own solution to a Challenge Question, but the CTO didn't even look at my source, he passed it to his engineer who found that it failed test. That meant that I was not invited in for an on-site interview.

What gets me down is that I had a partial solution that would have passed all the tests had I persisted, but I felt that it was stylistically poor so I rewrote the entire thing from scratch. That would have worked but by writing the entire program twice, I didn't leave myself enough time for adequate testing.