Stop comparing your work and your accomplishments to those around you. While competition may be healthy in terms of motivating a person to achieve their highest potential, comparing yourself to others is unnecessary. Everyone is on their own trip, taking things as they come for how they are, and making the most of the life they were given. The truth is, there will always be people who you will strive to emanate; whether it be the work they create or the vibes they give off, the fact of the matter is, you are a unique and special individual. Never before has there been a person exactly like you, nor will there ever be again. Free yourself from the illusions of comparisons, and viewing yourself as sub-par in terms of other people's standards.
Stop thinking that things would be so much better if you could just draw, write, photograph, sing, etc., better than the next person. While you should hold yourself to a certain set of standards to ensure you're reaching your highest potential, never think that you aren't good enough because "someone else is better." The world desperately needs thinkers, and artists, and dreamers, and creators, and building a mental prison in your mind by comparing yourself to others does nothing but keep you grounded when you should be discovering your wings and using them to soar. There are certain qualities about you that are uniquely wonderful that are YOURS and yours alone. Be the best you that you can be, and don't hold yourself back for the sake of "not being good enough."
Stop thinking that things would, could, should be better if one event had or hadn't happened to you. Good and bad days are merely illusions; lingering in the past merely makes us nostalgic. We see things from the past in a different light than how they really were, while anticipating the future solely makes us anxious. There is only here and now, so let it be. Do what you can with today and know that everything is susceptible to change. The truth is, we barely have (if any) control over the things that come our way in life, but we do have control over how we react and move forward. Let hardships make you better, not bitter.
Start reveling in your unique YOU-ness. Don't hold your productivity to other people's standards. F. Scott Fitzgerald published his first novel at 23; though you might be in your twenties, you still find yourself trying to figure out who you are and where you belong, and that is okay. It's not a competition, despite being deemed the human race. Essentially, there is no such thing as winners and losers - so long as we all get there. Take the time to appreciate your accomplishments, as well as who and how you are as a person. Be the best you that you can be, and just know how special you truly are.