"Why are they lifting more than me? Why did she get a pull-up before I did? Why am I struggling to reach my goal when everyone around seems to be getting better?"
We all do it. We all compare ourselves to those around us. Maybe it's out of fear, out of anxiety, out of competition. Whatever it is we've all looked at another human being and compared our skills and traits with theirs. Much like fast-food, cutting corners, and excuses, that needs to STOP.
If you don't know 100% of their background, then you don't know what advantage or disadvantage they may have. They may be younger. They may have an athletic background. They may put in twice as much effort in the gym and in the kitchen and that may be helping with their lifts, their runs, their workouts, and their progress with the health and fitness. Don't focus on what "could be" when their habits and background have no effect on you and your performance inside and outside the gym.
On the other hand, they may be older. They may have never played sports or stuck with a workout program before in their entire life. They may be struggling just to get to the gym 2-3 times a week. If you are pleased with your progress because you feel you are doing "better" than them, I encourage you to focus on yourself. Focus on your own life, your own goals, and your own variables. Where could you have better focus on your own health and fitness goals? Could you eat better? Could you make it 4 times a week instead of 3? Could you spend less time THINKING that you are better than someone else, and more time working hard to be better than you were yesterday?
In class I always encourage people to track their workouts and their progress. I don't do it to congratulate those who have the heaviest lift of the day, or to put the fastest member on a pedestal. I encourage everyone to track their workouts to measure THEIR OWN fitness. Sure, if you've got a "swole-mate" or a "barbell bro" it can be fun to compare numbers to motivate and encourage each other, but tracking workouts should be about measuring your own fitness. Look at your own data, find where you are lacking and take action. Stop comparing your fitness journey with everyone else's, and start putting in the work.
Focus. Work hard. Push yourself to be BETTER EVERY DAY.