Symmetric vs asymmetric cryptography

Symmetric

One secret key locks and unlocks (AES, ChaCha20). Fast — ideal for bulk data — but every party must already share the secret. Distributing that secret safely is the hard part (the Ring cannot be mailed to every ally).

Asymmetric

A keypair: public key may be posted on the walls of Minas Tirith; private key stays with you. Encrypt to a public key (or verify a signature) without ever shipping a shared password. Slower than AES, so real systems hybridize: asymmetric wraps a random symmetric session key.