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?
It isn't advisable but it should come in handy instead of going to the place where you hide your seeds only to open up your wallet but we shouldn't be confident with how good our memory was, so it is always safe to have a back up. Write it down in something sturdy so that it will survive any hazardous elements. Some vaults are also strong and I think not all of them are expensive, especially the smaller ones.
The only thing that boggles me is that when we say vault. The first thing will then came to our mind is money and other valuable items. Criminals and even the normal person knows this. They will always be after it once they see it so I still prefer to keep my keys in a secret location instead.