I use two types of notebooks. One where I don't care about structure or content. I just write whatever I'm thinking about as I think it when tackling hard or la

I use two types of notebooks. One where I don't care about structure or content. I just write whatever I'm thinking about as I think it when tackling hard or large problems. Kind of like an unstructured unspecific mind-map. I find going back to this is highly effective to get me back into almost the exact frame of mind up to a couple of years later. Then I have project notebooks, where each page is dedicated to one project. I only take it out after spending some time in the mind-map kind and I have made enough progress that it's worth writing in the project one. This notebook is written as documentation for an imaginary third party. It's useful for sharing with others and more importantly myself in the further future. I use this system for work and personal projects and while I don't too often have projects running long enough for this to matter I regularly refer to my old solutions and thoughts. It has definitely prevented me from walking in proverbial circles.