YAGNI is short for You Ain’t Gonna Need It and is a reminder (a mantra) that warns you away from providing solutions for problems that are not (yet) manifest - and may never be.
It works under the belief that predictions of the future are inherently risky and, more often than not, build on sand (“too little data, too many assumptions”). Given this, making plans for potentials now is in the way of already creating a solution for the definite - and is therefore bad. Worse: it delays getting better data, better feedback with which assumptions could be validated and with which the shape of the real solution could be found. So: don’t do it.
The term originates from (extreme) programming, where it is used to reject adding functionality that would not be used, yet.
