Proof

In mathematics, it is really hard to prove things.
Almost 75 years ago, a mathematician name Collatz made a conjecture,  that seem pretty simple.
He said take any number. If it's even, divide it by two. If it's odd, multiply it by three and add one. Then repeat. He said no matter what number you started with, you'd end up at 1 eventually.
As it turns out, no one has been able to prove it.
But it has been tested a lot. In fact, it's been tested for almost 6 billion billion different numbers, and it's worked for every one of them.
That's a lot of tests.
If everyone on the planet tested one of these every second, it would take 27 years for us to test that many.
Funny thing is, mathematicians don't really care how many tests you've run.
They want proof.