When Sherlock says he doesn't know 

why Molly can't say ILY to him

 (Sherlock meta by writingwife-83)

Q: Molly says that she can't say "I love you" to Sherlock, and that he knew why, but Sherlock denies it and says he doesn't know why. Do you think he lied or genuinely did not know why she wouldn't say it to him?

A: I don’t think he was lying at that moment. I think he honestly didn’t understand why she couldn’t just say it. Because in his mind it was already established that she loved him. It wasn’t a secret. So he simply wanted her to say the words. And actually, it’s obvious that his initial attempt was to get her to say them WITHOUT the meaning behind them. Basically just a “repeat after me” idea. But that’s where he was at first still thinking too much with his head.

I said this before in another post, (and also in my post TFP fic) but the problem with that is that those aren’t just meaningless words. If you say them to someone and mean it, they’re very emotionally powerful. It’s a powerful experience to hear it said to you but also to speak it, especially the first time! My belief is that he didn’t fully grasp that till she made him say it first. Which, to me, proves their truth from his lips. If he spoke those 3 words without the hard hitting truth behind them, I really don’t think he would have felt the need to shred a coffin with his bare hands immediately afterward.

So basically, once again, Molly Hooper schooled him.