Except when sometimes it does. That is, external factors reveal old bugs or introduce new ones. Like when you use it after installing a new package/driver/OS and it blows up. Or after years you give it to a new crazy user which somehow succeeds it hitting 20 keys at a time and your code doesn't handle that. I'm not saying occasions like those require a complete rewrite, just that it's not because code has been fine for 10years that it is bugfree and needs no more work ever. (though in cases like this switching to a proven lib for handling key input if such a thing even exist might be a solution - which then introduces new problems like more dependencies and bugs in that lib making your own software not working properly and so on and so on:)