a cover is not the book
A cover is not the book means the outside looks good but the inside is a hot mess. Like when you get a cupcake and it's just frosting and a sad cake.
He had a perfect Instagram. Now he's just a guy who eats cereal for dinner.
That guy had a cool logo. Now he's just a dude who screams at his cat.
That band had a sick poster. Now they just play in basements and scream at each other.