What is YAGNI?

Don't buy insurance you will never need. Keep your resources available for the highest priorities. Stay light, so you can move nimbly when necessity commands. Don't generalize hastily, lest you end up with vast, empty conceptualizations. Let yourself refactor when it serves several specific purposes.

You Ain't Gonna Need It (YAGNI): Always implement things when you actually need them, never when you just foresee that you need them.

Even if you're totally, totally, totally sure that you'll need a feature later on, don't implement it now. Usually, it'll turn out either a) you don't need it after all, or b) what you actually need is quite different from what you foresaw needing earlier.