Trying to do everything at once may not be possible and it's exhausting. It's akin to a hamster running in its wheel and going nowhere. Well for the purpose of exercising it's great for the hamster but may not be so great for people.
Some of us like to compare ourselves to others who appear to be hugely successful in many life endeavors and that can inspire us to become greater.
But what if you're not sure of yourself and what if you lack confidence. Well, all I can say is to never doubt yourself or your capabilities. No matter how small some of us may judge our talents or contributions to be, we never know the extent to which our actions affect/effect change in people either directly or indirectly. A thought, a word or an act can leave lasting impressions on others and that in itself is very powerful. And that power comes from you. Believe in your greatness and don't underestimate who you are and what you can do.