The statement you provided is actually the other way around. Newtonian physics, also known as classical mechanics, is applicable to macroscopic objects and everyday phenomena, while Einstein's theory of relativity, specifically the theory of general relativity, is necessary to accurately describe the behavior of massive objects, extreme speeds, and gravitational interactions.
The reason why Newtonian physics works well for macroscopic objects is because it provides a sufficiently accurate approximation in the realm of everyday experiences. Newton's laws of motion and his theory of universal gravitation are highly successful in predicting the motion of objects such as cars, projectiles, and planets, where speeds are much lower than the speed of light and gravitational effects are relatively weak.
However, as objects approach speeds comparable to the speed of light or when they are subjected to intense gravitational fields, Newtonian physics fails to provide accurate predictions. This is where Einstein's theory of relativity becomes necessary. The theory of special relativity, developed by Einstein in 1905, describes the behavior of objects moving at high speeds and shows that the laws of physics are consistent for all observers in inertial frames of reference.
Moreover, Einstein's theory of general relativity, formulated in 1915, extends the principles of special relativity to include gravity. It provides a more comprehensive understanding of gravity as the curvature of spacetime caused by the presence of mass and energy. General relativity has been experimentally confirmed in various scenarios, such as the bending of light around massive objects and the predictions of the existence of black holes.
In summary, Newtonian physics is suitable for describing everyday objects and phenomena at low speeds and weak gravitational fields, while Einstein's theories of relativity are necessary to accurately describe the behavior of objects at high speeds, strong gravitational fields, and in extreme scenarios.