Good cryptography should be auditable, that means it should be simple. It should not rely on experts knowing their way through the complexity but should rely on mathematical guarantees.

Yes the cryptography primitives should act like black boxes, no need to peak inside but when a number of these black boxes are used together to form a high level protocol allot of subtle things can go wrong for example see the history of SSL/TLS https://www.feistyduck.com/ssl-tls-and-pki-history/