Why would (spoiler) insist on attacking Winterfell right now (S06E08)?

Question

Earlier in Season 6 of Game of Thrones, we saw

Jon quite disaffected with his duties

and essentially walking off the scene for some soulful reflective rest and relaxation. Sansa had to really work hard (well, sort of) to get him to go along with her plan to

mount an attack on Winterfell.

As we see

Jon

coming before the heads of prospective supporters, he does not seem very enthusiastic or passionate - and he doesn't even describe the White Walker Zombie Army threat as a central motivation (although

Davos

does).

Then comes the scene in Episode 8 where he essentially decides, against the counsel of Sansa even, that the time has come to make their attack.

So the questions are:

1. Why the sudden change of heart, with him now clamoring for an attack?
2. Assuming he does not know something that we don't, no ace up his sleeve or anything (which seems like a reasonable assumption considering his behavior so far) - why would he prefer attacking immediately rather than in a few more weeks, after possibly securing Tully or maybe Manderly forces?
3. Under the same assumption, what makes him believe he stands a good chance of winning this battle?
4. Even if Jon wins, an open-field battle - rather than some sort of combination between a siege and guerilla tactics - will at the very least exact heavy losses on both sides. How is that reasonable considering

they're expecting to be faced with White Walkers and Zombies later on? I realize they can't take on the WWZ army anyway, but may well be able to mount some kind of defense at the wall, say.

So what's the deal here? Am I missing something?

Answer 1

You are forgetting about the "come and see" letter...

Ramsay is threatening action against Rickon, Sansa, Jon, the Wildlings, and even the Watch itself.

There is no getting around confronting Ramsay.

If they do not gather forces and march south, Ramsay is going to march north.... This was the turning point for Jon, he knew he had no other option and waiting around was not going to do him any good.

Let us also not forget... WINTER IS COMING.

Seriously, the snow was one the reason Stannis' army was slowed down. The deeper the snow gets the less likely Jon will be able to mount a successful attack because it would be more likely that Ramsay would just hole up in Winterfell. Ramsay wanted to meet Jon in the field because he did not want to appear weak, but the more winter comes the more foolish it is to venture outside the walls.

Jon also has no idea when the White Walkers and Night's King will attack the Wall. He needs to have the North reunited by that time to have any hope of a defense against the army of the dead (as Davos reminded Lady Mormont).