I saw this explained well in a book called The Phoenix Project. The book talks about what software development can learn from decades of manufacturing process improvements.
This blog post shows the graph presented by the book, which makes a similar but more general point to yours and further formalizes the Slack concept.
Seems it’s hard to pin down the source of this concept, but it apparently follows from Little’s Law.
References seem to be missing? It’s too bad the new site doesn’t have a good way to do footnotes.
This is really great stuff, thanks for posting—I’ve only had time to skim, but I plan to start at the beginning and give some more detailed feedback. This is all right in line with what I’ve increasingly felt is missing from my (unfortunately) casual study of rationality: putting concepts to practice.