People are inherently good at comparisons. If you look at a pile of eight bottle caps you will not know how many are there unless you count them, but if there is a stack five bottle caps next to it you will immediately know which pile is bigger.
Relative size is very important to us and it makes sense when you think about how important decision making is for survival. If you’re trying to pick a place to sleep between two options it’s more important that you pick the safer of the two places than that you quantify the exact difference.
But, thinking comparatively has downsides.
The reason the people at the gym are in better shape than you is because they are the people who spend the most time at the gym. If the people around you are in better shape than you are the chances are there is at least a correlative effect between where you are and your physical health. By the same token if your friends are all smarter or richer than you, you may be putting yourself on the road to becoming smarter or richer, or you’re a waiter at a fancy restaurant.