i still don't know why lancel decided to follow some random kid in the sewers when he was sent to get cersei.
Because you had to think that just like Margaery's telepathy, they were *this* close to averting catastrophe.
Cersei could have chosen virtually any other time to blow up the sept and probably kill the high sparrow as well his core leadership, accomplishing her goals and even killing Margaery in the process if she wanted to.