I once worked with two great interns. By themselves, they were better than the average intern. But sit them down side-by-side at one terminal, and give them a tiny amount of design advice, and they morphed into a good senior programmer. They could follow a tricky refactoring through 20-year-old C++ code with only a vague roadmap, and turn a vile mess into nicely organized code.

It only goes to show just how good Microsoft's recruiting used to be—we lost the pair of them to Microsoft the next summer, just as we did the rest of our very best interns.