If we're weaving together three strands (basic braid), that's fine - we've got three interactions. If we take that braid and two more and weave them together, IHMO we're only adding three more interactions (now we're at 6), but if we take all nine original strands and weave them all together, we're up to, what... at least 72 "interactions" (each of the 9 has an interaction with 8 others), and that's before asking if any of the "interactions" themselves become "interacting things" (and then we get a combinatorial explosion).

If instead we take those nine, and, say, braid three together for a bit, then swap one strand out for another, braid for a bit, repeat until we've gone through all nine - each strand is interacting with, hmm... 4 others? (two, then a new one, then a second new one) So then that's "36".

It's not really a precise measurement, but I do find it useful question both when investigating a system, and when designing one: "how many things are interacting, and how can I reduce that?" (systemic complexity), followed by "how can I simplify the interactions themselves?" (abstraction leakage), followed by "how can I simplify the things?" (cleaning up well-encapsulated code).

A practical example: If I want to create a test factory for an object, how many other related objects must I create for that first one to exist in a valid state?

A practical application: I can get away with complexity in well-encapsulated code, because it's easy to come back to and fix; I won't have to modify anything "outside". But I can't get away with complexity between things, because then in order to come back and fix it, I have to deal with chunks of the entire system.