Sorry if this makes no sense.
MIKA wrote this song about a cab driver he once met who told MIKA about how he had fought in war. He said that he had no physical injuries in the war so everyone said he was lucky, but they didn't understand that he was broken on the inside from the things he'd seen. I think that's where the line "And you don't understand why no one else can see" came from. The man told MIKA that he sometimes wanted to die because of how traumatized he was which i guess is where the line "Walk with the devil in your head, You would think you were better off dead" came from.