it's the easiest thing in the world to do.

Anyone can give up,  it's the easiest thing in the world to do. 
But to hold it together when everyone else would understand if you fell apart, 
that's true strength.

Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time.
Thomas A. Edison

“I'm not saying it's going to be easy. Nothing in life is easy. But that's no reason to give up. You'll be surprised what you can accomplish if you set your mind to it.After all, you only have one life, so you should try to make the most of it.” - Louis Sachar, Holes

“Giving up smoking is the easiest thing in the world. I know because I've done it thousands of times.” 
- Mark Twain