There will always be someone better, faster, stronger and better looking than you.
No matter who you are, you will always be able to compare yourself to someone else and feel miserable in the process. Self-improvement means you're running your own race, start focusing more on you, and less on others.
Focus on your strengths. Focus on your weaknesses. Focus on your goals.
It's easy to get caught up in what we 'can't do', especially when we rarely take time to be grateful for what we can. Spend less time envying someone else's highlight reel and more time crafting your own.
The grass is always greener when you're not the one mowing it.