Her reasons for leaving were 'obvious'. = It's 'obvious' why she left.
You are stating 'the obvious'. Tell me something I don't already know.
Her doctor immediately noticed the 'obvious' signs of the disease.
(..) you listen to me right now! Do you remember what Cho said about Rowena Ravenclaw's diadem? There is not a person alive who's seen it. It's obvious, isn't it? We have to talk to someone who's dead. It's very impressive, isn't it? If you've to find her, you'll find her down there. (..)2011 Harry Potter and the Deathly Hallows: Part 2