After publication in 1905 of his Special Relativity,
Einstein was praised but he also got a lot of criticism. Paul Ehrenfest, Mach and others revealed inconsistencies.
Einstein listened to them and made crucial improvements in 1916 so that the famous paradoxes disappeared.
It formed the basis for his General Relativity.
However till today the old version of SR is still taught to students including the paradoxes of the twins, the ladder, etcetera . Those who don’t know of Einstein’s change of mind, struggle on or come up with myths.
This article helps you to learn the way out as Einstein did himself.