It is a capital mistake to theorize before one has data.

The world is full of obvious things which nobody by any chance ever observes.

Of all ghosts the ghosts of our old loves are the worst.

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.

So swift, silent and furtive were his movements like those of a trained bloodhound picking out a scent, that I could not but think what a terrible criminal he would have made had he turned his energy and sagacity against the law instead of exerting them in its defense. -Dr. Watson, The Sign of the Four

When people bury treasure nowadays they do it in the Post-Office bank.

Ah! my dear Watson, there we come into those realms of conjecture, where the most logical mind may be at fault. Sherlock Holmes speaking with Dr. Watson.