WHAT'S THE POINT
Usually Sam Winchester wasn't one to be slow on the uptake. But when it came to his brother, sometimes he had a blind spot the size of Brazil. He'd been through Hell and back – literally, and more than once – and he just wanted everything between the brothers to be all right.
Being in their Bunker home seemed to settle Dean, so they stayed. Now that Cas lived with them it was another thing that seemed to settle Dean – their adopted angelic brother was good company to both of them.
After the few years of hell that was Dean bearing the Mark of Cain and then the Darkness being unleashed on their world, their mother Mary was back with them. That seemed to settle Dean even more – he had the bit of his childhood back, his innocence returned.
But then, Mary left, to "find herself" and her place in a world she barely understood. And it was like watching the darkness descend upon Dean again. But he didn't talk about it, so Sam assumed he was handling it okay.
And Sam's blind spot kicked in. He didn't even notice that Dean had stopped talking all together.
Until two days later, when Cas walked up to Sam and asked if Dean was angry with him.
Then Sam thought back over the last few days – and realised that Dean wasn't just not talking to Cas. He wasn't talking at all!
Sam had Cas check Dean out thoroughly. No curses were present. No possession. No spells that Cas could tell. No illnesses or angelic persuasion.
Sam had a gigantic blind spot toward his brother. He had forgotten, over a decade earlier, when Dean had told a tragedy-muted little boy that after Mary had died he hadn't felt like talking for awhile.
Sam had not seen that this was just history repeating itself.
After all – what's the point of talking when nobody was listening?