I worked on a code (DOCK for docking drugs into molecules) that had a core routine (a preprocessing step) written in ancient FORTRAN by a genius professor. He

I worked on a code (DOCK for docking drugs into molecules) that had a core routine (a preprocessing step) written in ancient FORTRAN by a genius professor. He couldn't explain why it worked, even though he had written the paper and the code. Everybody who looked at it gave up. Eventually somebody invented an all new algorithm for the preprocessing and wrote it in C++ (comprehensibly) and the old routine was retired, to everybody's satisfaction.