The life of being the best friend

We all know and love our main characters, i know i do at least, but we tend to always shine the spotlight on them and forget our side and supporting characters including....the best friend. In many anime/manga/book series/tv show/etc. our main character goes off on their adventure, meets new people an everything but they leave various people behind including their best friends. I know that this is not true for all anime/manga/book series/etc. but for the majority(at least from the ones ive seen and reading) the best friend does get left behind.
(A/N:i apologize in advance if this is really bad but plz read feedback is always appreciated ^_^)