Criteria for defining errors of a physical theory are formulated. It is shown that the Special Theory of Relativity (STR) has a solid mathematical basis. An enormous amount of experiments carried out in particle physics use beams of particles having a very high energy. The data of these experiments are consistent with STR and support our confidence that STR is an excellent theory. Several specific cases of this issue are discussed explicitly. Contrary to a common belief, it is proved that the contemporary mainstream of physicists adhere to some theoretical ideas that violate STR.