This is why everyone should create an emergency kit, so if you forget your master password, it wouldn’t be the end of the world.
Depending on the password manager and the KDF that it uses, you could even get away with just a 4-word master password, so it shouldn’t be too difficult to remember. And when you type it out regularly during the first week or so, you should be able to remember it. But an alternative could be creating your master password using this website that was recently shared on the forum, if you feel like a regular passphrase is too difficult for you to remember.