Usage patterns
〈人〉は楽天的な性格だsomeone has an optimistic personality
He has an optimistic personality and bounces back quickly even after failing.
楽天的に考えるto think optimistically about something
I try to think optimistically about the future.
楽天的な見方をするto take an optimistic view (of something)
She's the kind of person who takes an optimistic view of everything.