I agree that the sacrifices have to be meaningful or at least leave you with a feeling of hope.

The story ought to dictate its ending. Sometimes it will be happy, unhappy, resolved, or unresolved.

Sideways didn’t resolve anything really, but it did show the start of a new story arc and a meaningful change in its central character.

The Proposition ended well on one level, but completely devastatingly on another.

Bliss (both the Australian movie and its source novel by Peter Carey) ended in death, which turned out to be a very happy ending.

In the end the main character getting lobotomized is the ultimate victory on the part of authority to take away his free will.

But I think that ending is satisfying because we know the hero is fighting a losing battle from the beginning. The storytellers propose the thesis that authority is ruthless, and will not tolerate free will. They establish this premise early on, and I always felt that was just as much if not a stronger part of the story than the actual plot.

Hero getting a lobotomy just confirms everything we believe about the evils of authority figures. “I told you so!” – Therefore satisfying.

Now if they hadn’t focused so much on nurse Ratched’s battles with the hero Randle, and hadn’t emphasized his constant testing of her and really drove that theme home, then Randle’s lobotomy at the end would seem senseless and confusing.

It’s also the nature of the setting. They’re in a mental institution. Randle could escape at any time, but he chooses to be there. He doesn’t so much want to be free (he could just leave) as he wants to be free in the face of authority.

In a sense he creates his own doom. That combined with confirming the audience suspicions about authority creates an ending which justifies everything we know to be true.

The story just has to make sense, and extreme events that happen need to have happened for a reason, even if that reason is not apparent until the end.