Intellectual effort, when conducted without books or notes, gives an entirely different sensation than when carried out under normal conditions. One's involuntary memory acts much more forcefully, the memory of which Proust speaks and which he considered to be the sole source of literary creation. After a certain amount of time, things surface in our consciousness, details we hadn't had the slightest idea were even 'stored' anywhere in our brain. What is more, those memories that come from our subconscious are more deeply rooted, more intimately bound up with one another, more personal.