Pairs behind you (mathematics)

[Red_Diamond]

One rule of thumb I remember from Chip was when starting with a pair, always look at how many up cards are BEHIND you. The magic number was 2 or more = DON'T RAISE.

I also read in other literature that this is a solid rule to play by.

However, what I have never seen, is even a simple mathematical model to explain why the cut-off number is 2. I had assumed back in the day that it was a simple rule of thumb, but by now I'm positive there must be some sort of mathematics behind it.

I just have never seen it.