DRY Principle Study Portal

TL;DR

DRY ("Don't Repeat Yourself") says every piece of knowledge in a system should have one authoritative representation, so a requirement change only needs editing in one place. The senior nuance is that it targets knowledge duplication, not textual lookalikes — the AHA principle ("Avoid Hasty Abstractions") and the Rule of Three guard against the opposite failure mode of merging two things that only happen to look the same today and will diverge tomorrow.