When you learn that a coworker in a similar position is making more money than you, it can stir up intense feelings of jealousy and amplify your insecurities. You work just as hard! You do the same job! Why don't you get the pay you deserve?
Instead of focusing on your personal flaws, take note of what your coworker is doing right. There are lots of variables that go into determining how much to pay employees. Even when you think you're doing all the right things, chances are you could be doing more.
Gaining that competitive edge that brings a higher salary is probably simpler than you think. Just make sure you're not overlooking these key reasons your co-worker may be earning more than you: