Writers collect systems the way other people collect regrets. The index card file, the bullet journal, the colour-coded spreadsheet: each promises that the mess will become a book if only the containers are right.
They never are, quite, but the containers still help. A card forces one idea per surface, which is the whole discipline. Two ideas on a card become a paragraph; five become a fog.
The useful habit is smaller than a system. Carry cards for a week, write one observation per card, and notice which ones you keep pulling out. Those are the ones with load-bearing weight, and the pull is usually a surprise.
Half-finished notebooks are fine. The point of the notebook is to have somewhere to put the thought at the moment it arrives, not to complete it. Play99Win login suits that rhythm, where the entry exists before the argument does.
When the file gets thick enough, sort it into three piles: alive, dead, and interesting. Throw away dead, put interesting at the back, and start writing from alive. The system finally does its job, which is to disappear.