I never make exceptions. An exception disproves the rule.

One should always look for a possible alternative and provide against it. It is the first rule of criminal investigation.

To every rule there is an exception—and an idiot ready to demonstrate it. Don't be the one!

As a rule, said Holmes, the more bizarre a thing is the less mysterious it proves to be. It is your commonplace, featureless crimes which are really puzzling, just as a commonplace face is the most difficult to identify.

Skill is fine, and genius is splendid, but the right contacts are more valuable than either.

You have probably never heard of Professor Moriarty? said he.