I`ll share something. my very bestfriend we were friends when we were still young until now.we are studiying in the same school.the fact that I knew she is my true friend is because she corrects me in my mistakes and tries to understand me as I am. another one.one of my friends(classmate)she sacrifised our friendship because of her ex.i will not elaborate it more.but that`s why I call a plastic friend. that`s according to my experience.