I love Molly. She’s so ordinary; and yet she’s not a shallow character. I love this moment because Sherlock realizes he’s underestimated her observation skills and just stands there, speechless, outdone by little Molly Hooper; and you can tell from his face that he knows what she just said is true, and he almost looks guilty that he’s been unkind to her. I love how Molly brings out the humanity and compassion in Sherlock. (scene gifset)
But notice...Molly is the exception. Not only is she in his heart, but she is a vital figure in his mind palace. Just this once, Sherlock broke his rule. And just as she's done so many times before, Molly Hooper saved his life.