Isaac Newton formulated the law of universal gravitation which explained the motion of all celestial bodies in space known at his time. Also, he demonstrated that it is the same law that is causing everyday objects to fall to Earth.
Newton wrote that he had not been able to discover the reason for the phenomenon of gravity. Flat-Earthers use this as “proof” that he lied and he did not know anything about gravity, and that gravity was a mere fabrication. They are wrong. Gravity adequately explained the motion of all celestial bodies and the fact that everyday objects are falling to Earth. Newton simply did not know what is causing it.