With everyone sharing all the things on the internet all the time, it's really hard not to play the comparison game. This applies as much to your everyday life as it does your athletic endeavours. One of my favorite mantras for running has always been to "run your own race."
Remember, even if you get the sense that the people you follow online are sharing everything, they aren't. They are curating their content to convey a certain message. Even if part of that message is being real, uncensored, and sharing the "messy parts" of their life, it's still not the whole picture.
The same is true when it comes to athletics. There will always be someone out there who can run faster than you, lift heavier weights than you, or who is more flexible than you. If there wasn't, you'd be an Olympic gold medalist in running, weight lifting, or gymnastics/diving (anything that requires lots of flexibility). Even if you are at that level, chances are, someone else will have beaten you at some point because you were off your mental game, your internal environment was off (you ate too many french fries at dinner the night before), or the external conditions were something you weren't prepared for (I've trained for many races in the cold only to die in the heat on race day).
The best thing you can do is run your own race at your own pace. Whether this is related to a weight loss goal, a dietary change, and athletic performance goal, or something completely different, you do you. If you are constantly judging yourself against the success of others, you'll never celebrate your own successes. Because, as I said before, there will always be someone better/faster/stronger than you out there. When you "run your own race," you find ways to celebrate success. Whether you run faster than you did yesterday, feel better slogging up that giant hill, or only ate half a bag of chocolate chips instead of the whole bag, THAT IS SUCCESS.
There is also something to be said for connecting with real people in trying to reach your goals. One of the places that I have felt the most supported and least judged in my goals and progress is in the training groups I participate in. Specifically my swim group. We are broken up into lanes based on our speed. We are not all the same speed within a lane, there is definitely a fastests person and a slowest person. But we all are there to accomplish the same workout, which is not done by comparing ourselves to the people in other lanes. We just push each other (or drag each other along depending on the day) to be better. So rather than being jealous of the person I follow online who swims 500 yards in 8 minutes, I am pushed and supported by all the people in my lane at swimming who swim 500 yards between 9 and 11 minutes.
I'm not suggesting that you shouldn't be motivated or inspired by what other people are doing. There is just a very fine line between being motivated/inspired by someone and feeling like they are more successful than you. If you fall on the wrong side of that line, maybe it's time to cut back on social media and go out and find your real life tribe of people who can help support you in your goals.
No matter what you do or how you do it, remember that in the end you need to run your own race, at your own pace. Not happy with your progress? Strive to do better next time instead of comparing yourself to someone else's success.