I can strip and clean and re-assemble a number of Lee-Enfield bolt action rifles, stripping and assembly I do blindfold, but when it comes to making a wormery or when to plant my winter crops I tend to go look it up as it isn't something I am familiar with. I used to run rifle ranges, I was very well versed in the orders to be given, but an "aide-memoir" was always in my hand.
There are many things we may need to do which we haven't had the need to do of late, as I read else where -
"our civilisation has the benefit of knowledge that has been accumulated since the beginning of time and yet most of us are less practical than Iron Age man."
All our knowledge is tied up in books and minds, minds will go when the people do, books will be around a lot longer.