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.
(..) -Who cares? An excellent idea to show them that, Professor Snape. . . . . .but if you don't mind me saying, it was obvious what you were about to do. lf l had wanted to stop you, it would have been only too easy. Perhaps it would be prudent to first teach the students. . . (..)2002 Harry Potter and the Chamber of Secrets