“It may be that you are not yourself luminous, but you are a conductor of light. Some people without possessing genius have a remarkable power of stimulating it.”

Sherlock Holmes compliments his friend, Dr. John Watson, on his ability to bring out the essentials of a difficult problem with his thoughts and questions. Watson, whose stories about Holmes become the detective’s professional biography, often serves as a sounding board for Holmes’s ideas and speculations. The quote establishes the essential relationship between Watson and Holmes: The doctor is the genius detective’s intellectual sidekick.

“I am afraid, my dear Watson, that most of your conclusions were erroneous. When I said that you stimulated me I meant, to be frank, that in noting your fallacies I was occasionally guided towards the truth.”

Having complimented Watson on his ability to bring out the detective’s best, Holmes then rewinds the praise and replaces it with what is almost an insult. It is as if Holmes cannot really admit how much Watson’s friendship means to him, so he takes it back. To give Holmes credit, he may mean only to clarify his original compliment (see Quote #1, above), but his critique of Watson makes the doctor seem like a useless fool. It is true that Holmes is head and shoulders above nearly everyone at deduction and inference, and it is not wrong for him to know he is the best, but it may be a social flaw to say so.