What small change made the biggest difference to your daily energy?

The changes people report most consistently are unglamorous: a fixed wake time, morning daylight, breaking up long sitting, protein at breakfast rather than only carbohydrates, and stopping caffeine by early afternoon. What links them is that each addresses a system rather than a symptom — circadian timing, blood sugar stability, or circulation. Contrast that with the things people try first, which are usually supplements and energy drinks that address neither. If you want to test one, choose a single change, keep it for two weeks, and judge it against how you feel at 4pm rather than how you feel doing it.