I read that one of the best ways to preserve a seed phrase is to write it on a piece of paper and keep it in a safe place... Somewhere safe could be in your home out of the reach of family members and friends, it could also be a safe deposit box. But not everyone are financially buoyant to afford the services of a deposit box.
I believe we must have seen or heard about fire outbreaks, where buildings are completely erased by fire. Imagine if the owner or occupant of such a building has some Bitcoin assets, and has his/her phone, tablet, laptop and the seed phrase piece of paper in the building and everything was lost to fire. Now, this brings me to the question... Can seed phrase be memorized? It's advisable to memorize seed phrase?
There's no universal best way, it all depends on what kind of threat you think is the most likely. If you worry about other people in your house stealing your coins - you should store your seed or wallet file in encrypted format. If you worry about a house fire and can't get a fire-proof safe - you should find additional place to story a backup of your seed.
Memorizing your seed is a bad backup option, our memory wasn't created to store random data perfectly, even remembering 12 words in order is a challenge for us. How it will look on practice is that even if you have no problems with memorizing it, in the long run you will likely forget parts of your seed, potentially making it unrecoverable.