After a particularly gruelling day at a crime scene, Sherlock almost driving the new assistant Anderson was training, to tears twice, John decided it would be best to return home.
Sherlock sulked during the cab ride until he came to his brilliant conclusion. "Human can never have acatalepsy," Sherlock declared. "They're simply too stupid. As long as there are people like Anderson in the world, even with all my genius, we can't have any hope."
John only sighed, and closed his eyes, hoping the cab driver couldn't hear. He didn't want to be thrown out. Again.