The human behavioral repertoire is surprisingly small
Theoretically you could do almost anything at any time. In practice, most people cycle through a small set of behaviors — the same things, roughly the same times, under the same circumstances. When bored, most people have about three to five defaults. Someone with ten would be an adventurous outlier.
Imagine a rat cage furnished with levers — each lever is a behavior in the repertoire. Some cages have only one lever (and it's for heroin or something). Other cages have more: play video game, send tweet, talk to other rat, cook dinner. The levers available and the order in which they get pulled determine felt experience of life, moment to moment.
Behaviors interlock — exercise sharpens appetite for food, satiety enables rest — so the repertoire is better understood as an ecology than a list. It's complex enough to resist top-down planning, but it's a small system. That makes it tractable.
The behaviors that take up most of a person's time are a tiny subset of what's possible. The repertoire, not the schedule, is the unit worth improving.
Source claim: Most people's lives are shaped by a surprisingly small set of recurring behaviors — roughly 3–5 — making the behavioral repertoire a tractable system to work with.