Uber-designer Michael Bierut talks about the 85 notebooks that he's carried around over the last 26 years (not all at once, of course).
The notebooks function like a security blanket for me. I can't go into a meeting unless I have my current notebook in my hand, even if I never open it. Because I carry one everywhere, I tend to misplace them a lot. Losing one makes me frantic. Everyone who works with me gets used to me asking, "Have you seen my notebook anywhere?" which I assume gets irritating after a while: sorry. I've left them behind in clients' offices. On one occasion, I left one on the roof of a cab on the upper west side. I ended up walking ten blocks, retracing the taxi's route, until I found it on Broadway at 63rd Street, intact except for some tire marks.
I've tried using notebooks several times over the years, but the habit has never stuck.