2. Major Barrymore's Password
This deduction is significant just because it is something that we all wish we could do. We've all been there. Either you're trying to log in to your friends Facebook in order to leave a rude message on their wall or you're trying to crack their iPhone passcode to take funny pictures on their phone. We all wish we could crack the passwords of our friends. In the series two episode, The Hound of Baskerville, Sherlock does exactly that. He needs the password of the head of the Baskerville research facility, Major Barrymore. He sits in his office, where he would have sat to think up his password, and looks around at eye level to find the key. Several separate biographies of Margaret Thatcher later and Sherlock realises that the password could only be 'Maggie'. This deduction qualifies for this list by virtue of being something we all wish we could do. It all seems so simple, if only it was that easy in real life!