A lot of things can be derived from more basic or at least more beautiful principles. It makes perfect sense to say that Schroedinger&#x27;s equation can be derived from Lagrangian Mechanics, even if this is not historically how it happened.<p>An especially beautiful constraint is &quot;Schroedinger&#x27;s equation has to be linear because otherwise you can build a (quantum) computer that can solve NP-complete problems in polynomial time&quot;. Schroedinger did not know about NP-completeness, but this notion does give us clues why the equation is what it is.<p>It is always instructive to see how a &quot;fundamental&quot; law can be derived or at least constrained from other laws. Thermodynamics and the notion of entropy would not have been invented if engineers did not &quot;rederive&quot; what was considered fundamental at the time.