The four daily habits that matter most

Why these four

Large prospective cohort studies of lifestyle and longevity keep landing on the same short list: what you eat, how much you move, whether you smoke or drink heavily, and how you sleep. Those are the levers with the most evidence behind them and the most day-to-day control attached.

Hydration rarely makes those headline lists on its own, but it's the one that changes how the day feels fastest — even mild dehydration has been shown to affect mood, alertness and perceived effort.

They're a system, not four separate projects

Sleep is the upstream one. Experimental sleep restriction is associated with increased appetite and higher intake of energy-dense food, and a poor night reliably makes training feel harder. So a red sleep light on Tuesday often explains a red eat light on Wednesday.

Movement runs the other way: regular physical activity is associated with better sleep quality. Once you see all four side by side for a month, the causal chains in your own week become obvious in a way that tracking one habit alone never reveals.

What 'good' looks like, roughly

Useful anchors rather than rules — adjust to your body and your doctor's advice:

• • Sleep — 7–9 hours for most adults, with a consistent wake time doing more work than a consistent bedtime.
• • Move — at least 150 minutes of moderate activity a week, plus breaking up long sitting stretches.
• • Eat — mostly whole foods, enough protein and fibre, and a bar you can hit on a bad day, not just a good one.
• • Drink — roughly 2–2.5 litres of fluid a day for most people; more in heat, illness or hard exercise.

Why four is the limit

Habit formation is slow for effortful behaviours — often a couple of months per habit. Attention is the scarce resource, so ten tracked habits usually means ten half-attempts.

Four is also the point at which a daily check-in stays under a minute. If reflection takes longer than that, it becomes the thing you skip when the day was bad — which is exactly the day the record was worth keeping.

How to track them without the spreadsheet

Three Lights is built around exactly this: the four habits come as standard, and each gets one light per day — green, yellow or red. It takes about fifteen seconds, and the month view shows you the interactions rather than four isolated numbers.

If you later want a fifth habit — meditation, reading, no-alcohol days — Pro adds custom habits. But the four are the foundation, and most people never need more.