I've been working on fixing some old C++ code at my company so that it compiles with the most recent version of the compiler. To my surprise, the errors that the new compiler gives me are very reasonable. But I always ask myself, "how on earth did this ever compile in the first place?"

The crazy part is going into the commit logs and seeing that a lot of the people who wrote this have been very successful. They've become vice presidents, retired rich, and written influential papers.