UmbraClaw

Exactly my point. Sherlock may be brilliant, but he's also arrogant, and actively tries to hide/deny it when he makes a mistake. He may have gone in with the assumption that there would be an off switch, then didn't spot it at first.

It seems that not everyone may have gotten the same twist out of the ending that I did, so allow me to shed a little light on an interpretation which might suit the good Gatiss style better. If you go back and watch the bomb disarm scene, you will notice that Sherlock changes demeanour slightly right after the bomb reaches 1:29, and he sits up. From then on, he is no longer talking about the bomb, but rather about him not being able to apologise properly to Watson. Every one of Sherlock's sentences from then on fits that interpretation, and he doesn't immediately consider that Watson may not pick up on it. Which he obviously doesn't. After the cutback to the third explanation, we return to a Sherlock who's just realised that Watson hasn't realised the misunderstanding, and is in tears laughing about it. He takes the opportunity to pretend he was merely yanking Watson's leg, rather than admitting to his 'moment of inperfection', in a way grasping the unexpected chance to roll back his admission that he was sorry and that there was something he did not know how to do (apologise). This may not be Sherlock's most shining moment, but he is only just beginning to experience and deal with his friendship emotions, and he is overcome by his own pride. This crosstalk technique, playing to the expectations of the audience, and requiring a bit of digging to spot, is evident again a bit later, where Watson mentions his gravesite speech, then doesn't realise that Sherlock is talking literally when he answers that he was there, and that he listened, rather than metaphorically. We as audience, know Sherlock was there, so that is of course the first interpretation we jump to as well, but the second one is there as well, evident in Watson's reaction.