Avoid over-engineering a solution

The idea behind YAGNI is that you should only implement functionality when you need it and not just because you think you may need it some day. Ron Jeffries, one of the co-founders of XP, once said:

"Always implement things when you actually need them, never when you just foresee that you need them."

Following the YAGNI principle helps you to avoid over-engineering a solution. You don't want to spend time on future scenarios that are unknown. The problem with implementing a feature that you think might eventually be needed is that quite often the feature ends up not being needed or the requirements for it change.

Code that is not written equates to time and money that is saved. Spending time and money on a feature you don't need takes away from time and money you could have spent on something that you do need. Resources are finite, and using them on something that is unnecessary is a waste. As was the case with code duplication, adding unnecessary logic to an application increases its size and complexity, which reduces maintainability.