There is always someone who looks better, has bigger arms, better abs, or more perfectly shaped pecs. Don’t get caught up in the comparison game. Everyone is on their own path and all that matters is what YOU have done with your body.
Each of us starts from a different place and with different gifts. Some of those huge muscle guys in the gym showed great potential for size and strength when they were very young. We can be jealous of their genetic gifts, but it’s counter-productive to dwell on this. No matter where you started, you have something that is to your advantage. Everyone has a body part that responds well to training, plus we each have plenty of other gifts and talents not related to our physique. Your body is part of who you are, but not ALL of who you are.
What matters is the progress YOU have made with your own physique. Take pictures from time to time so you have a clear reference point for your progress. The mirror can be an unreliable meter for our progress because we see ourselves every day and even tend to not see what we’re actually looking at. (Some days I look in the mirror and see Arnold, and other days I see that shrimpy kid from Junior High.)
Stay focused on your own path, and use those that have already accomplished more as sources of inspiration. What matters is what you have accomplished and the progress YOU have made. Be grateful that you are healthy, in the gym, and able to improve your body. Then get busy!