I've been working on a project with a co-author for nearly 2 years now and as far as I was concerned we were done with it. She kept tinkering with it but I was done. We would submit it for publication very soon, which involves a series of 4-5 reviewers picking it apart, verifying the math, and generally looking for holes.
Today I attempted to start a new project and pulled out a complicated formula from a section I had worked on for weeks and weeks. I plugged it into the new project and found....nonsense. Utter nonsense. I checked and rechecked and re-re-checked and re-re-re...well, you get the point.
Three hours later I found the mistake. And naturally it was at the very first point of the problem which means (blaalrlrgllle darllghhle) the whole thing needs to be re-solved.
Better that I found it than the reviewers. Or that it got published with a mistake. Better. Better. Better. (blllarragkladal)