A while ago one of my friends mentioned to me that they don't actively remember their eurocheque card security code, but they can enter it automatically, without thinking.

That made me think about my security code and I also couldn't remember! But the thought tripped me up so much, that I couldn't let it go and the next time I had to withdraw some cash, I didn't know what to put in. I actually had to return my card and get a new one a few days later. Now I make a conscious effort to think about what I am entering.