We all see seasons where some team, say Indiana, plays tough games but loses the close ones and ends up 4-8, which could have been 7-5 with a couple of breaks, and another, say Purdue, end up 8-4 but with some razor thin wins over mediocre teams and four considerable losses and with an easier slate than Indiana. The actual ranking of each should be about the same, perhaps around 50th or so, but they end up spread apart in any full ranking scheme because of record.
In the above, perhaps Indiana lost to OSU 45-35 and Purdue lost 63-9.
I've seen mediocre UGA teams go say 10-3, but the 10 wins were over mediocre teams and they got beat decisively when they played good teams. The numbers get them ranked, but the reality is that was a so-so team that could easily have been 7-6.