I felt Holmes's hand steal into mine and give me a reassuring shake. - Watson

When the impossible has been eliminated, all that remains no matter how improbable is possible.

Depend upon it, there is nothing so unnatural as the commonplace.

Well, sir, let us do what we can to curtail this visit, which can hardly be agreeable to you, and is inexpressibly irksome to me.

There are no crimes and no criminals in these days. What is the use of having brains in our profession? I know well that I have it in me to make my name famous. No man lives or has ever lived who has brought the same amount of study and of natural talent to the detection of crime which I have done. And what is the result? There is no crime to detect, or, at most, some bungling villainy with a motive so transparent that even a Scotland Yard official can see through it.

...it is only when a man goes out into the world with the thought that there are heroisms all round him, and with the desire all alive in his heart to follow any which may come within sight of him, that he breaks away... from the life he knows, and ventures forth into the wonderful mystic twilight land where lie the great adventures and the great rewards.

The more featureless and commonplace a crime is, the more difficult it is to bring it home.