What is the YAGNI principle and why is it important?

Explanation

YAGNI (You Aren't Gonna Need It) is a principle of extreme programming that states you should never implement functionality until it is actually needed. Predicting future requirements is unreliable, and speculative features add complexity, maintenance burden, and bugs without immediate value. YAGNI encourages: building only what is needed now, keeping design simple, and adding features when requirements are clear. It complements agile development and MVP approaches. However, YAGNI should not prevent reasonable architectural decisions that are hard to change later; use judgment to distinguish between necessary foundations and speculative features.