"No. Because I took your pulse. Elevated. Your pupils dilated. I imagine John Watson thinks love’s a mystery to me, but the chemistry is incredibly simple and very destructive. When we first met you told me that disguise is always a self portrait—how true of you. The combination to your safe, your measurements. But this, this is far more intimate. This is your heart. And you should never let it rule your head. You could have chosen any random number and walked out of here today with everything you worked for. But you just couldn’t resist it, could you? I’ve always assumed that love is a dangerous disadvantage. Thank you for the final proof."
Sherlock, A Scandal in Belgravia