Well, and there is the end of our little drama," I remarked, after we had sat some time smoking in silence. "I fear that it may be the last investigation in which I shall have the chance of studying your methods. Miss Morstan has done me the honour to accept me as a husband in prospective."
He gave a most dismal groan.

My name is Sherlock Holmes. It is my business to know what other people do not know.

You have been in Afghanistan I perceive.

I'm not a psychopath, I'm a high-functioning sociopath. Do your research.

They say that genius is an infinite capacity for taking pains," he remarked with a smile. "It's a very bad definition, but it does apply to detective work.

It is cocaine," he said, "a seven-per-cent solution. Would you
care to try it?"
"No, indeed," I answered brusquely. "My constitution has not got
over the Afghan campaign yet. I cannot afford to throw any extra
strain upon it."
He smiled at my vehemence. "Perhaps you are right, Watson," he
said. "I suppose that its influence is physically a bad one. I find
it, however, so transcendently stimulating and clarifying to the
mind that its secondary action is a matter of small moment.