The Little Shit That Could
When you have a piece of shit that takes forever to squeeze out of your bunghole. After sitting on the crapper for 10 to 15 minutes you begin to push harder and harder, saying to yourself or out loud "I think I can, I think I can." repeatedly until you finally shit it out.
He sat on the crapper for about 20 minutes, and pushed and pushed as if he was going into labor screaming "I think I can, I think I can!", until the little shit that could finally dropped into the toilet.