I don't know why I had those two convictions. I arrived at BBN with no skill per se, but I had those principles in the back of my head for some reason. I thought I ought to be able to understand anything and it shouldn't be so hard. I found that even for the time-sharing system and the IMPs—for all of those class of programs, that proved to be true. In general once I had the right understanding of what a program was supposed to do, the pieces would fall into place. The pieces that didn't belong would stand out like a miscolored piece in a jigsaw puzzle.

Another principle was I always wanted clean listings. I wanted the thing to be just right. When you have to fix a bug in a program you never, ever fix the bug in the place where you find it. My rule is, “If you knew then what you know now about the fact that this piece of code is broken, how would you have organized this piece of the routine?” What were you thinking about wrong before? Fix the code so that can't happen. When you finish with a routine I want every routine you work on to look as if it was just written. I do not want to see any evidence of afterthoughts or things gone wrong followed by something to correct the error or a mysterious piece of code saying, “This routine returns the wrong value every now and then so I've got to fix it.” I don't want to see any of that. I want to see code that looks like through some divine inspiration you got it exactly right the first time.