BIP39 (Mnemonic Recovery Seed Phrase) is Bitcoin Improvement Proposal. Instead of memorizing a private key with a lot of characters, you should memorize 12 or 24 words you are familiar with.

The increase in words will be good but a lot of words will make the matter the opposite. The missed or lost word will increase and thus you will need to memorize it in digital form, which is aware of the increased risk.