Ideas do not arrive from nowhere; they arrive from a warehouse you have been filling without noticing. Which is why people who make things tend to be people who collect things — overheard remarks, a photograph of a badly designed sign, the way a stranger described their job.
The collecting looks like procrastination. It is raw material, and nobody can tell in advance which fragment will turn out to be load-bearing.
The only real requirement is somewhere to put it. A note made on a phone in a waiting room counts. Most of what gets written down is useless, and the whole method depends on not knowing which.