Before turning to those moral and mental aspects of the matter which present the greatest difficulties, let the inquirer begin by mastering more elementary problems.

I think you want a little unofficial help. Three undetected murders in one year won't do, Lestrade. But you handled the Molesey Mystery with less than your usual - that's to say, you handled it fairly well.

His incredible untidiness, his addiction to music at strange hours, his occasional revolver practice within doors, his weird and often malodorous scientific experiments, and the atmosphere of violence and danger which hung around him made him the very worst tenant in London.

It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.

No man burdens his mind with small matters unless he has some very good reason for doing so.

There is nothing more deceptive than an obvious fact.

It is stupidity rather than courage to refuse to recognize danger when it is close upon you.