That’s a good quote, and frankly, I agree with it, but that doesn’t dispute at all what the OP wrote.
Some things we won’t know until we try. Other things are very provable through (what I call God’s rule of) Math. Einstein’s work was based on that math.
However, there is more math to do to figure out on this issue for sure.
We really don't know what we don't know. And some things are beyond our present comprehension. Scientific theories and postulates have changed over time despite the "math."
For example, the Heisenberg Uncertainty Principle states that you can never simultaneously know the exact position and the exact speed of an object. Why not? Because everything in the universe behaves like both a particle and a wave at the same time.