Designing something good for me means going through at least 11 seriously bad approaches before half understanding the problem and having a half-working solution. Trying to use a notebook to aid a learning or research process at all has always meant wasting a lot of time "perfecting" those bad approaches. And ending up with lots of notes that document nothing but a painful struggle to make sense. Looking back through the notes that I did take, in notebooks that I have been gifted over the years, is almost unbearable. The approaches I tried before arriving at the right one were fundamentally wrong, there is no fixing them, and it's painfully obvious when looking back. Aside from the emotional problems I perceive there, it's obvious to me that there is no engineering value in keeping those notes at all.
The current best design always lives in my head, and by the time it exists, the solution and understanding is so clear and detailed that I can't be arsed to write it down.
I do think there is value in taking notes for others, though.
What works a little bit for me is having a lose stack of papers at work. The topmost paper serves to put a coffee mug on top, that will take the coffee stains so the table stays clean. From time to time I actually scribble something on a sheet, and since the sheets are all loose it's very easy to discard any sheet after it's served its (diminishingly small) purpose as a thinking aid.