''... one man cannot do it all...''- Harry Gordon Selfridge
Yes, you can't do it all. But do not let what you cannot do distract you from what you can do. Instead of focusing on what you cannot do, 
instead of focusing on your mistakes, instead of letting what you cannot do discourage you, why not use them to motivate yourself?

Because there are lots of things out there that we cannot do. But if you want success, if you want growth, then don't waste your energy on what you cannot do. 
Instead, focus on what you can do. And do it really well. Why is that? Because no one is going to pay you for doing an average work. 

Success comes from doing things really well. Whatever you are doing, do it really well. Do not let your fears distract you from giving your best. If you can't give your best, then ask for help. 
Because ''one man cannot do it all.''