Why are people so caught up in a record?

Example people think Rocky Marciano is the greatest fighter ever because he was 49-0. Some people think the 72 Dolphins are the greatest because they went 17-0. Before the Bulls went 72-10 the record was 69-13 by a Wilt & West led Lakers team & people didn't talk about them as the greatest. In your opinion who is the greatest boxer, greatest NFL team & greatest NBA team regardless of record & why?