The Challenge of Capturing a Random Idea

I remember reading an interview somewhere with ryan holiday, the author of a several books on stoicism. And i'm wondering if that's the way in which you're using things like index cards. And you also talk about digital notes. Is there like a structure around projects, or is this more free form? It's structure on projects. I'll have like a stack with a binder clip on it. Then i'll look at old categories of cards that i might have and then try to see if there’s any correlation between the two ideas.