After you meet someone, the odds they think of you slide toward zero unless periodic, valuable touchpoints push the line back up.
The idea
Right after a great lunch, you're at 100% mindshare: if something relevant comes up, they think of you. Then their inbox, calendar and feed fill up with newer people (the last coffee, the last text, cousin Bruce's idiot son "who just needs a chance"), and the line slides toward zero. My coach Patrick Ewers walks through it in the book with a lunch with Mike, and about ten years ago I drew the curve for one of the many investor decks I've had to put together. It's not their fault. Memory decays. Each touchpoint spikes the line back up, and the more value it carries, the slower the fall afterward. How high you need to stay depends on what you might want later: a wave on the street needs very little, a referral needs more, an introduction that costs them reputation needs the most.
How to do it
Pick the relationships you'd hate to lose.
Give each group a fallback rhythm so nobody drifts under the line by accident.
Make each touch attributable and, when you can, useful.
Invest more in the people you might one day ask for something big.
Example
The National Association of Realtors found 88% of buyers say they'd use their agent again. Only 12% do. In the book I tell of Nancy, a DC agent who bumps into a past client at a neighborhood BBQ and learns he bought his next home with another agent. He. Simply. Forgot.
Watch out for
Blaming them. When someone says "I wish I'd thought of you," you're the one who dropped the ball.
Waiting for the perfect cadence. Nobody knows a relationship's half-life, so just keep the line moving up.
The Down Escalator: Every relationship rides a down escalator, so ending one just means stepping off; stop investing, decline politely, never ghost, and leave the door open.
CAPITAL: Timely Engagement: The T in CAPITAL. Give each group of people a fallback rhythm, then react to events, so prioritized relationships never quietly fade.
Something Is Better Than Nothing: Any touch they can attribute to you beats silence. If you don't know what to say, say anything.
Add Value, Don't Just Follow Up: Nobody wants to be followed up with. Treat the follow-up as your cue, and make the touch leave the other person better off.