The almost enormous mistake.

Which, even though it is not the best portmanteau I've come up with, I want to call it a 'megastake'... you know, a really big mistake. It was simple oversight to be sure. Something anybody could have done. But it would have been quite disastrous for me if it was not fixed through the caring efforts of my parents as it had been. Simply put, don't leave your main tool of work operation behind... ever... that is all.