Nothing is worse than having an itch you can never scratch! — Blade Runner

You have to accept that some things are beyond your control, that there are some wrongs that you cannot right, and that there are some goals you will not attain.  That’s a fact of life, not an excuse.  Recognizing that, though, should spur you to doing all you can.  Maybe you can’t feed every hungry person in the world, but you can make sure that those around you never go without.  You may not ever be the best shooter or the best artist or the best musician in your group, but you can still put in the hours and take what improvement you can make.  You will never rid the world of injustice, but you can stand up to it whenever you encounter it.

Knowing that you are not omnipotent or omniscient doesn’t relieve you from doing the right thing.  You just have to do the best you can with what you have.