You make dozens of decisions every hour, hundreds every day. Each of those decisions uses up a little bit of energy in the brain. Even apparently trivial decisions use up energy: latte or cappuccino? small, medium or large? drink in or take out?
The more decisions you make in a given time frame, the more your decision-making energy is depleted. You are more likely to decide on the default choice, the easier choice, the habitual choice. It takes less effort to choose it, and to follow it up.
This has two important implications for anyone who aims to have at least a little control in how they live their life.
Firstly, invest some effort in cultivating good habits, whatever good habits means for you: flossing your teeth before bed, smiling at people, writing thank-you notes, remembering jokes, whatever. The more embedded the habit, the more automatic it is and the less energy you will use up deciding choose it and do it every time.
Secondly, make your important decisions when you’re feeling fresh. For most people it’s not the evening, after a day of work. Evening is the time when people find it hardest to decide against “just another” helping of food, glass of drink, or hour of TV.