I wouldn't trust my mind to store seeds, the brain works in a very unreliable way, from there come the infinite types of biases we have, our mind takes the information we have and interprets it as it wants, maybe what you remember today as pears and apples, tomorrow your brain will make you believe with complete certainty that they were oranges and lemons, the two words that you forgot.
I think this kind of thing is just an optional thing where if we really want and are able to then we can memorize but when the situation is not possible then it won't be a problem if we don't remember the seeds we have because we can still write them down and keep them in a place that we think is safe.
This kind of option is only functioned to make it easier or make conditions more flexible I think when we write and memorize it then when at one time we want to open the wallet we have but don't carry notes then we can still use our memory for that but in the end at some moments this is also not an obligation so I say this as optional.
I don't remember my seed but I still keep it in a safe place so it doesn't matter to me even if I don't remember it because I have an archive that can still open my wallet with the notes that I secured earlier.