Esther Schindler writes "Baseball players can compare their excellence by looking at statistics. Developers... not so much. It's hard to know how good you are unless you go head-to-head with other programmers, which is one reason that programming competitions are fun. So, too, is the money you might win, or the career bragging rights, or, as Steven Vaughan-Nichols points out in 8 Contests and Challenges You Can't Resist, you might get to contribute to a NASA project. Wouldn't that look cool on your resume?" Link to Original Source
If it happens once, it's a bug. If it happens twice, it's a feature.
If it happens more than twice, it's a design philosophy.