Comparison with others

Why is there a belief that we should stop comparing ourselves to others?

What’s more, if you haven’t reached zen yet, you’re unlikely to be able to stop doing it at all. When you compare yourself to people you think are better than you, you have something to strive for. You want to become like them or even better. This motivates you to grow. If you compare yourself to those worse than you, it boosts your self-esteem.

If I compare myself to who I was yesterday, rather than to others, how will I know which rung of the social ladder I’m on? Or do I not need to know my place in society?