Physical storage is correct. The risk of any digital storage or network storage is much higher than that of physical storage.
A cheap sheet of metal can be carved more safely with a carving knife than write paper.
Don't trust memory too much, people's memory is quite insecure. Most people can't remember what they had for dinner yesterday.
Any electronic product has the risk of breaking. Never think that it is safe to store it offline in a flash drive(SD card/SSD).
The problem is not just the material you use, but where you keep it. Most people don't have a safe at home (and even if they do, it's not 100% secure). Metal or not, your physical seed can be lost, stolen, burnt...
Most people can remember many the names of persons (2 or 3 complex words) for decades. I don't see why they could not remember 3 or 4 simple dictionary words.
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A safe is an obvious target, why is it considered safe to place it in a safe? Everyone has their own method of storing items, and usually adding a passphrase is much safer.
The human brain has a hard time remembering random things, even just twelve random words.Even a random eight-letter password is impossible for most people to remember.
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