Please enlighten me.....Satchel Paige said, "Don't look back....Something may be gaining on you."?

And this statement has been given it's place among aphorisms. Alongside those of Mark Twain, for ex.....Well....To my thick mind.....I would think.....If you look back, and see something gaining on you......that would be an incentive to run (or try) harder. But that doesn't seem to be the accepted meaning of this quote. Help me understand....I appeal to those of you who possess much greater understanding than myself.........Thanks.