Yeah, several notebooks would cause a problem. I have ONE notebook that I use 95% of the time. It's a handy size, pocketable. I just bring it with. Writing notes down on your phone takes second place to a paper notebook. Just having the phone around can be problematic sometime. Especially if you're with other people. 

Signal312

Design

Fess up, where do you all get your best ideas? 

cryotosensei

How did you internalise the habit of carrying this notebook with you everywhere?

I do that too, but I kinda have several workbooks at several places. Which can get a bit disorganised at times haha