You usually don't have to make changes to code once you've written it? The only time I ever find that true is when the code is throwaway (ad hoc data crunching for some purpose, scripts to automate some one time tedious process, practice projects just intense to learn a system, etc). I don't think I've ever written anything that was useful for more than, say, a week that didn't get changed later by myself or someone else.

The typical claim is that code maintenance is at least 10x as long as the initial write.