The point of running numerical simulations is that when they come out wrong, you learn something. If you simulate this, for example, and get a different answer, you’ve learned that you’ve misunderstood the claim.

In other cases, a numerical simulation giving a wrong answer can quickly tell you that your apparently valid reasoning contains a mistake. That’s really useful, because subtle reasoning errors are really easy to make, and math is full of fun false proofs.

A wrong simulation is strong evidence that you’ve misunderstood something, and so by necessity, a correct simulation is (weaker) evidence that you’ve understood correctly.