I think a big part of it is swagger. You have to have the confidence in yourself and your team to go out and play the 3rd the same way you played the first. To go out and be aggressive when it's late and you have a lead, I think, goes against a lot of players basic makeup of wanting to protect that lead and not blow it.
Brining in Kane and making the playoffs is important for the younger guys because of this, imo. We want them to play like winners, then actually winning something is probably a good place to start.
I agree that this is part of it. But there's a wide spectrum available here. It's not as if the only options in the third period are, "step on their necks and bury them" and, "I'm scared of the puck".
Every one of these players has gone through multiple tiers of hockey, with multiple coaching styles. It's not a foreign language to them, adapting strategy to the situation at hand. And the one thing that confuses me the most is Lalonde - he came from Tampa, whose ENTIRE STYLE was predicated on the perfect balance of solid defense and dangerous counter punching when the opponent made a mistake. That's not at all the same as completely turtling up when you have a lead, so where's that element now that he's in Detroit? I understand the personnel isn't the same, but if the guys here are good enough to get a 5-1 lead, then they're certainly good enough to execute a better system of closing out a game than what we've seen.
Even if confidence could use a boost, it's mind boggling that all these professional players and staff seem to have zero nuance. Hire a damn consultant if need be, but this "light switch hockey" is a horrible way to approach defending a lead.