No Silver Bullet and Brooks's Law
Essential vs accidental complexity, and why adding people to a late project makes it later.
Software-Engineering
Conway's Law
Systems mirror the communication structure of the organizations that build them. Empirical, not proven — and the inverse maneuver as its practical use.
Hyrum's Law and Postel's Principle
Every observable behavior of your API is depended upon by someone; and the robustness principle that made that worse, plus the modern case against it.