The first example that comes to mind...
- lonely lad sitting on the porch swing
- lad and lass cuddled on the porch swing
- lad and lass drumming fingers on the arm rests as her young brother regales them with his day's adventures
Or if you are a devotee of that esoteric art of bridge:
- 1 person drumming his fingers
- 2 people drumming fingers
- 3 people drumming fingers
- 4 people in a lively game kicking each other under the table
The change in fun is not proportional to the change in the number of people.
On the serious side: somehow the third helping doesn't give quite the same satisfaction that the first did. We're not very fond of temperance; we even have an industry set up to try to drive it out of us. ("It's OK to go a little wild" sponsored by Ho Chunk Casinos) But fun isn't linear...
(*)I'm only on page 13. He seems to be working to prove fairly obvious things, and letting knottier things slide, and all without examples. I like examples. He probably does too, but the traditions must be upheld, I guess.