No one can be made stronger that doesn't first agree to meet one's own weakness. No one can become wiser without first agreeing to meet one's own ignorance. But the fact of a transcending strength and wisdom is only proven in the face of weakness and ignorance; which means running away from any painful limitation is the same as agreeing to live as its prisoner. Never forget this one last fact: left unattended, weakness and ignorance grow stronger by themselves.
Here's the real reason why it's so important to always go the "extra mile" -- to do what you don't want to do, or feel like you can't do -- whenever it comes to your Work to be free: there is no other way for you to make contact with, and then call upon, an indwelling limitless resource that will only reveal itself to you... after you've expired your own.