Disclaimers: These characters do not belong to me.
Sam was the physic.
Sam was the one that demon wanted to add to his growing army.
As Missouri was constantly reminding him, Sam was the special one. The Winchester brother who had a big role to play in the final battle. To his own mind, Sam was special but he was not very special. No one person could ever defeat a big ass evil on there lonesome. It took people who helped those gifted with a big role in fates final lay to help win the battle.
He could have told Missouri that if you take away a persons support base they crumble.
Whether he knew it or not Sam depended on those around him. When Sam was younger and before he had hit his teens there dad was someone Sam depended on. Then anger played a part and there dad was no longer a person Sam depended on. Then he became the one Sam depended on. The anger did not separate them it just drew them closer together. It made Sam more aware of his powers and a lot more confident in using them.
He thinks about telling Missouri that Sam's new found confidence in his abilities is though a good support base but he does not waste his breath. Missouri has her set views on Sam and his role in the final big battle. He is not going to be the one to spoil Missouri view of Sam.