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.
(..) trying to catch a fish for lunch. Jo, fish. I want you to look like you're fishing. I'm trying, but I've never fished before. That's quite obvious. You might just as well be flying a kite. Don't look like such an amateur. You're just not fishing. I am, but it's caught on something. (..)1957 Funny Face