I am convinced that past and future exist.

My philosophy teacher teaches me the core concepts of the Theory of Special Relativity, Theory of General Relativity and Theory of Quantum mechanics. Being the student of mathematics, it was very astonishing for me to hear the concept of Theory of Special Relativity, at the first time. Initially, I thought that how can two observers observe same event on different time? It maybe there is going something wrong. I am still partially agreed with the Theory of Special Relativity.
The reasons can be;
Maybe our devices are inaccurate?
Maybe it is not giving unique answer for different observers?
Maybe the effect of Theory of Special Relativity is very small in our daily-life?
Maybe something else? But I am trying my best to understand the core concept related to the Theory.

Speed of light is constant