Legend has it that an apple falling from a tree and then subsequently hitting Isaac Newton on the head is said to have provided Newton the idea of the gravitational force. This is a well-known and often told legend in physics.
There is a lesser-known legend that explains Einstein’s discovery of his theory of the gravitational field. One day, while walking on the street, Einstein witnessed a construction worker fall from the roof and landed on a pile of straw without sustaining any injury. Einstein questioned him if on the way down he had felt the tug of the “force” of gravity. When he was told that no force had tugged, Einstein realized that “gravitation” can be replaced by an acceleration of the observer’s reference system.