- Seed phrases should never be memorized, nor written on a mobile device or computer. They can be written on paper or in a book that shouldn't be visible to external members and should be strongly protected.
Remember, ink can fade over time
https://bbs.boingboing.net/t/which-inks-fade-fastest/96814And this is why you make multiple copies and store them somewhere safe, create new ones after a certain amount of time and repeat the process until you die or probably be unable to do it. It's a pretty straightforward approach to keep your funds safe, and even if inks fade, it will take a long ass time for it to do so, and you will always have time to replace those writings and create new copies of your seed/passphrase.