Paper can be really fragile, and all it takes is a tear or water spill or defacing to deny you access to your BTC forever.
So, you should make a second copy of your seed phrase that is identical to the first, and store it on a different place from the first seed so that they both cannot go down together except in extreme circumstances like a natural disaster.
Well, this advice is far from new. But indeed, it's good to remind people now and then about it (I would have been expecting this in B&H though).
is remembering 12 words that hard?
It's not.. until it is. Just imagine a stroke, or a (motor)bike crash, or many other things the can happen to you.
Plus, mind is a very strange thing. In a year or two you will be certain the 5th word in your seed is "about" and in reality it was always "above".
So no. It's not difficult to keep in mind 12 words for a while. But the longer that while is, the more chances for something to go wrong.