Your mind. It’s so placid. Straightforward. Barely used. Mine’s like an engine, racing out of control. A rocket, tearing itself to pieces trapped on the launch pad. I need a case!
Tʜᴀᴛ’s ᴛʜᴇ ғʀᴀɪʟᴛʏ ᴏғ ɢᴇɴɪᴜs, Jᴏʜɴ. Iᴛ ɴᴇᴇᴅs ᴀɴ ᴀᴜᴅɪᴇɴᴄᴇ.
Don’t make people into heroes.
There is no great genius without a mixture of madness.
When Moriarty shakes Sherlock’s hand at the end, Sherlock cocks his head in a slightly puzzled manner, looking at him in confusion… at least, that’s what you realise when you notice that Moriarty used his right hand to shake hands with him, despite being left-handed (as we see earlier in the episode, with the teacup). Moriarty left his main hand free to grab his gun and kill himself, and Sherlock has just enough time to notice that.