To take the discussion on a slight tangent, how uncommon is this phenomenon? An applied tool works really well but nobody knows why. I can give another example from the domain of formal verification: SAT solvers which are at the core of most modern verification&#x2F;synthesis tools.<p>You can download open source SAT solvers today that work spectacularly well on &quot;real&quot; SAT instances with millions and millions of variables and clauses. Yes, SAT is the quintessential NP-complete problem and in fact it is pretty easy to come up with a SAT instance with only a few tens of variables&#x2F;clauses that would kill these solvers. But somehow these &quot;hard&quot; instances almost never occur in practical problems generated in hardware&#x2F;software verification&#x2F;synthesis as well as ton of other applications (planning, constraint programming etc.)<p>So this must there is some characteristic of the problems that we generate in practice that makes them &quot;easy&quot; but we don&#x27;t have a good understanding of what this characteristic is. All we know, for now, is that we&#x27;ve somehow stumbled upon a near-perfect set of heuristics that work amazingly well on the SAT instances we encounter in practice.