Why real systems use both, not either one alone — one type is fast but hard to distribute safely, the other solves distribution but is too slow for bulk data.
Both are ways to encrypt — reversible, key-based confidentiality, as covered in the companion explainer on encryption vs. hashing vs. encoding. This explainer goes one level deeper, into the two fundamentally different types of encryption, and the very different problems each one solves. Symmetric encryption uses one single key for both encrypting and decrypting — whoever holds that key can do both. Asymmetric encryptionuses a mathematically linked pair of keys — a public one that only encrypts, and a private one that alone can decrypt. They aren't competing options where one is simply "better." Each one solves exactly the problem the other one creates — which is why every secure system you actually use, like HTTPS, uses both together, not either one exclusively.