If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.

This quote encourages people to not give up when facing difficulties. It says that if you cannot do something, you should try something else that you can do. Even if that means just making very small progress, you should still keep going. In other words, you should never let obstacles stop you from moving forward towards your goals.