Backwards practicing

I have always practiced all my major scales pretty much every day. But this week I started playing from the top going down instead of my usual way, starting at the bottom going up a couple of octaves.  Who would've thought this would be complicated any way? I am surprised that even though I have played these exact notes on the way down nearly every day for four decades, when I start at the top I really have to think about what comes next! Who would've thought I had neglected such an easy thing. I guess there really is no limit to what I can practice.