Comparing yourself to others is, generally, not a good idea. You forget to focus on your own goals, you become jealous -- you can even start to feel ungrateful for what you have. But there's another reason to avoid this habit: you could be measuring yourself against a false standard.
Financial writer Carl Richards explains that we often compare ourselves to others without actually knowing the detail of their situation. This can cloud our judgment and lead to poor decision making. He writes:
It's hard not to compare ourselves to others based on visible spending or consumption because it is often the only yardstick available. Psychologists refer to this as social comparison theory. When an objective measurement isn't an option, we compare ourselves to what we see around us...But our desire for validation comes with some serious blind spots. Income is relative to so many other factors that both the number of dollars earned and how they appear to be spent make for a worthless comparison. Your neighbour may drive an older car so he can retire early. Your cousin may earn $100,000 a year compared to your $50,000, but it comes with a two-hour commute and weekend commitments. We simply don't know.
When you make assumptions, you might craft your own goals and habits around those assumptions. For example, maybe your frugal neighbour drives a cheap car, so you're turned off of frugality, because you assume he or she is poor.
The bottom line: create your goals around your own situation and your own numbers. A little comparison can be helpful sometimes, but take it too far, and you might lose track of what works for you. For more detail, check out the full story.
Comparisons With Others Can Obscure Our Own Goals [N.Y. Times]