I was recently studying some basics of quantum computing and had to re-learn a bunch of linear algebra. I thought I had forgotten everything, but when I sat dow

I was recently studying some basics of quantum computing and had to re-learn a bunch of linear algebra. I thought I had forgotten everything, but when I sat down to review the material I picked it up very quickly (much faster than when I was in undergrad). It was like riding a bike. I think we think we forget, but the knowledge is actually dormant and much easier to get back. So I don't think forgotten knowledge is wasted, it's still valuable.