Comparing our own lives to others often leads us to feelings of discontent, malaise, and wanting more. It makes us try to be someone else rather than accept ourselves for who we are. We try to change ourselves to be like those people we think are better, but really we are striving for an unrealistic ideal here.
We can't compare our lives to someone else because we can't possible know what their life is like.
a < b
If a = our life, and b = other person's life, can the above equation be true? Well, say we give our own life a value of 10 based on whatever factors there are (be it happiness, health, financial, whatever). We can't then come up with a value for someone else's life because it is an unknown.
10 < b
Is this a rational statement? Or what if we say someone else's life is worse than ours?
10 > b
Is this a correct statement? We can't compare an unknown value to a known value. It just doesn't work. So when we think someone else's life is better, they could be going through depression, or struggling financially, or experiencing similar feelings of discontent because they're comparing their selves with someone else too. Or if we judge someone as having a worse life, that person may be going through a hard time at this particular moment, or maybe they are perfectly content with their lives and we only think their life is worse because we have some pre-conceived idea that they need to have this wonderful thing we have or else they can't be happy.
Everyone in the world has such vastly individual experiences and yet we are so much the same in how we worry about how we stack up against the others. Rather than compare myself, I try to let things be the way they are and just be content.