Lane's death was definitely the Big Moment of the episode as Devin wrote, but what really crushed me was Glenn's line in the elevator with Don near the end: "Everything you think is going to make you happy just turns to crap."
Over at Slate they already pointed out that one sentence can be the fortune cookie recap description of this entire series, but man... in each of those moments it was just so fucking true that it was impossible to not look around my living room at everything that was supposed to make me happy at one point and then tell each one to go fuck itself. Fortunately my wife wasn't there at the time so she didn't have to deal with that Mad Men induced bummerfest, but my Mondo posters? They totally got the evil eye.
But at the same time, Don knows that the one way he can stay happy is if he keeps chasing that happiness. Because that's the thing with success - once you get a taste for it, you just want another bite. And Don is finally wanting another bite, so he gets that meeting with the Dow Chemical boys, and he just chews into them.
Was that his intended pitch? It certainly didn't feel rehearsed. And what about the general philosophy? Should Dow be happy with 51%, or should they be chasing 100% like Don wants to? It certainly makes business sense to chase the 100%, but then you're never going to be happy.
And maybe that's the best thing these characters can hope for. Maybe it's the best thing we can all hope for. If we just keep chasing happiness then we'll never have to be let down by finding out it's not all it's cracked up to be, right?
Well, I suppose Mr. Pryce would disagree...