Shutter Island ending explained

What happens

In the lighthouse, Dr. Cawley reveals that Teddy is really Andrew Laeddis, a patient. The investigation was a role-play to avoid a lobotomy. Teddy seems to accept it, then walks willingly toward the orderlies.

The last line

"Which would be worse, to live as a monster, or to die as a good man?"

Two readings

1 · Chosen oblivionSpeaking as Teddy again, he knowingly accepts the lobotomy rather than live with what he did.

2 · A real relapseThe delusion has returned, so the treatment has failed and he is taken away still believing it.

What it says

The film is about how a mind builds a bearable story around unbearable guilt. Ending on this question, rather than a verdict on Teddy's sanity, leaves you facing the choice too: a hard truth or a comforting lie.