I hear people say all the time that you only should focus on “running your own race” and not worry about what anyone else is doing. I agree that you need to turn your attention inward to be happiest with your effort (and, if applied correctly, with your results).
BUT we’re human and most people thrive on competition among other similarly-skilled individuals. If you’re working out with someone or next to someone, you’re much more likely to push yourself a little more to keep up with or to beat that person.
Having intrinsic motivation will lead to better consistency (like getting out of bed and going to the gym when you don’t feel like it). External motivation will lead to better results (once you’ve gotten to the gym). So while you shouldn’t rely on always needing to have external motivation, it’s a nice way to enhance your results.