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Memorizing the seed phrase will be okay if the person is really good in memorization.
For the seed being placed on any devices/documents/websites, I think it will be good to encrypt it rather than just putting the exact same words. Still both of these will not work for everyone, so I think people should stick on how can they properly manage to store their seeds.
No matter how good the memory is, it should not be completely trusted. Human memory is very fragile and the slightest injury or disease can destroy the information about seed phrase stored in memory. Even paper wallet can be better and more reliable in comparison. Even despite its vulnerability to fire, acids and other methods of destruction. But this can be fixed thanks to external storage, in the form of a metal capsule and a box. The disadvantages of one material can always be compensated by the properties of another.