Actually, a private key and a seed phrase have a lot in common: they are both a representation of a random number (entropy) that is used to generate public keys and addresses. The only distinct difference is that a private key is used directly for generating the corresponding key, whereas seed is more like input data for a specific function that generates many and many private keys that in turn result in public keys and addresses. Moreover, I believe you can still convert a private key to a human-readable format. After all, a private key is nothing else but a set of ones and zeroes, which can be represented as something humans can better understand and write down. For example, you can convert your private key to a seed phrase using the same BIP39 standard.


It depends. For example, if you take a software wallet and use it as an interface for your hardware wallet (so-called watch-only wallet), it won't have access to seed phrases or private keys.