"If you compare yourself with others, you may become vain or bitter; for always there will be greater & lesser persons than yourself."
Who hasn't compared themselves to someone else at some time or another? Even embedded within the question, is a comparison with others. The duality of "right/wrong" comes into play, in as much as, if what I am doing through my comparison, is to try and make myself feel better about myself - then you (or something about you) is found to be wrong, so that naturally that would make me right.
The opposite is also frequently employed, by putting others on a pedestal, it can continually reinforce beliefs of inadequacy, I hold toward myself.
While it's true we can all be "mirrors" for each other, there is nothing to be gained by pumping myself up or tearing myself down based on comparison with others. Though it can appear ever present, life is not a competition. If what I'm interested in doing, is to forward my own evolution, then I can use my own life as the bench mark for comparison.
It's not my business what other people are doing with their lives or how poorly or well, they are doing it. I don't need to be "the best" at something in order to enjoy it. It's a flimsy measure at the best of times. If I were to base my self worth on my perception that I'm so exceptional at, lets say, playing the guitar - the moment I realize there is someone more skilled than me (which is another perception) the basis for my self worth vanishes.
For the record I'm not an exceptional guitar player and don't consider myself "the best at anything." I suppose there's no one that could hold a candle, at being me - but then again, some days I'd wonder about that too!