What is that term that means someone is oblivious but it's a good thing they don't know it?

There's some term that means that someone's oblivious, they're in their own little world and don't know about the bad things going on, but it's a good thing because they couldn't handle it or it'd make them sad. I just can't remember the term. Please someone help?

Unaware. Blind. Absent Minded.