The problem I always run into when I try something like this, is that I mostly (there are exceptions) use paper as a data processing medium (as opposed to a data recording medium). Most of what I do on paper is messy, half-baked, wrong, turns out to be a false start, whatever. Once all that is fixed, what is left gets tidied up into some sort of digital form, usually program code. I don’t want all that mess in the capital-N Notebook, but it is hard to know when to switch from backs of envelopes to the Notebook.
I suppose there might be a value in stopping right before the tidying-up stage (or perhaps right after it) and summarise the steps that led up to it (including abandoned approaches, and why) into some sort of document but that, for me, would be a digital file somewhere, not paper.
> use paper as a data processing medium
I also do the same thing.
> I don’t want all that mess in the capital-N Notebook, but it is hard to know when to switch from backs of envelopes to the Notebook.
On the contrary, I want and enjoy recording my failures, false starts in these notebooks. These are important lessons. A culmination of "what not to do"s, or "Lessons Learnt" in NASA parlance.
My engineering notebooks are my messy garages with working things on the workbench and not working things in a pile at the corner, recording how I think, what I think, and what works / what not.
The code is the distilled version of what's working, the "second" prototype, and the polished product.
Creation is messy, and there's no running away from that. Keeping the mess in its own place allows incubation of nice things and diving back into the same mess to find parts which works beautifully elsewhere.
I prefer to embrace the suck and document it too.
I feel I could write a long response to every comment in this thread as notekeeping is something I consider critical. Knowing when to commit to “The capital-N Notebook” is something I’ve struggled with as well. What has been effective for me is to scribble daily on a marker/chalk/dry erase board and then transpose the final thought into “The Notebook” at the end of each day. This lets me format, err, mull, etc. and the final (sic clean) notebook still has enough granularity to retrace my thoughts in the med-to-long term.