nadateturbe
Still, a theory is not a fact.
A layman's "theory" is not a fact. It is an unproved possibility.
A scientists theory has been subjected to innumerable people trying to unprove it by exposing it to every test that can be applied to it, and duplicating the results of those tests on many other occasions.
A scientist's "theory" has been subjected to a lot of research and observation, and has stood up to being tested, the logic and mathematics involved have been repeatedly done by different people, and the experiments have been repeated again and again, with the same results.
Most people have heard of Pythagoras. He noticed that triangles with one 90-degree right-angle seemed to have a certain relationship in the lengths of the three sides. So he researched it for years, drawing right-angled triangles, measuring the sides, and analysing the relationships of their lengths. What he came up with was "Pythagoras' Theorem"
He proved what has been drummed into schoolchildren ever since - that if you multiple the length of the long side (opposite the right-angle) by itself, the result is the same as multiplying the length of each of the other sides by itself and adding those two numbers together. That is "The square on the hypotenuse of a right-angled triangle equals the sum of the squares on the other two sides This has been proved every time it was done.
At one time (up to recently, anyway!) I could have taken you through every step of the proof. To follow that proof, you would have had to already know some other facts to do with geometry and/or algebra, but I can assure you that it works.
There are more than 30 different ways to prove it, Some are here - brilliant.org/wiki/proofs-of-the-pythagorean-theorem/