When it is made
The phrase is recorded in the Okinawan longevity tradition that ran through the villages of the southern islands across many decades of the twentieth century. Researchers studying these villages in the postwar years noted that the elders at the table consistently stopped eating before they felt full, and that the rule was taught to children the way a table manner is taught — by example, across many meals, rather than as a single instruction. The habit sits inside the broader washoku pattern: small bowls, a few well-cooked dishes, rice and soup at the centre, the meal eaten slowly with the table set. The Okinawan evening meal typically ends a couple of hours before sleep, and the post-meal time is given to a slow walk or a quiet kitchen rather than a second plate. The point is the rhythm — the table, the pace, and the gap — and the tradition expects the rule to settle in across weeks of meals, not a single dinner.
Disclaimer
This is a gentle everyday table habit rather than a restrictive diet, and it sits well inside an ordinary eating life. Anyone with a history of disordered eating, or anyone who finds that eating-by-rule stirs up anxious or rigid patterns around meals, may find the eighty-percent target more of a strain than a help — for them, a relaxed small-bowl plate without the percentage is a safer starting point. If you are managing a medical condition that calls for a specific caloric or nutrient plan, run the change past your own clinician before making it a daily habit.