Please don't compare yourself to others at the gym. Comparison is one of the greatest causes of unhappiness in life. So don't do it. Your internal dialogue shouldn't be, "I wish I could lift as heavy as he does." Instead, you should be saying, "I'm so glad I'm pushing myself today. Every session at the gym is a success."
Set your own goals for what you want to achieve, and never use anyone else's criteria for how you should feel. This doesn't mean that you can't draw inspiration from others. It does mean that you are not afraid to be you.
Remember this formula:
Happiness = Do your best.
Unhappiness = Compare yourself to everyone else.