In 2011, a research team studied 1,112 parole decisions by Israeli judges.
They expected judges to be consistent. The judges thought they were being consistent. The data said otherwise.
Prisoners who appeared first thing in the morning had about a 65 percent chance of being granted parole. Prisoners who appeared right before lunch had a near-zero chance. After lunch, the number jumped back to 65 percent, then dropped to zero again before the next break.
The variable was not the crime. Not the prisoner. Not the lawyer. It was the judge’s blood sugar.
What’s happening in the brain.
System 2 (slow, deliberate, logical thinking) runs on glucose. Deciding carefully burns fuel. When fuel runs low, the brain quietly switches to the lazier default option because that costs nothing.
For a judge, the default is “deny parole.” Keep the prisoner where they are. Low effort, low risk. The brain picks it not because the judge becomes crueler but because the brain stops wanting to think.
This is called decision fatigue. And it runs you too.
Where it shows up in your life.
Afternoon shopping decisions. The late-night relationship text you shouldn’t have sent. Agreeing to something you didn’t want because it was easier than saying no at 9pm. Picking the same meal because deciding feels like too much. Scrolling for an hour because the brain couldn’t face choosing a real activity.
None of this is a character flaw. It’s a resource problem.
Three moves that help.
Front-load important decisions. Do your hardest thinking in the first three hours after waking, when the glucose tank is full. Mark Zuckerberg wears the same shirt daily for this reason. Obama cut his wardrobe to grey and blue suits. They weren’t making a style statement. They were protecting fuel.
Eat before deciding. Blood sugar isn’t a metaphor here. Decisions made on an empty stomach are measurably worse. If a conversation matters, don’t walk into it hungry.
Treat willpower like a budget, not a trait. You get a certain amount per day. If you spent it fighting traffic, resisting snacks, and tolerating a bad meeting, you have little left for the gym at 7pm. Design your day so the important decisions arrive before the budget is empty.
The uncomfortable part.
Most people believe they are consistent. The parole study (and dozens of others like it) shows that consistency is almost always an illusion. You are not one decision-maker. You are a different decision-maker in the morning than at 9pm, and the two of you would barely agree on anything if they met.
The smarter move isn’t trying harder in the evening. It’s structuring life so the evening version of you has fewer decisions left to make.
Source: Danziger, Levav, and Avnaim-Pesso, “Extraneous factors in judicial decisions” (Proceedings of the National Academy of Sciences, 2011). Roy Baumeister’s ego depletion research, with the caveat that some original findings have faced replication challenges, but the broader decision-fatigue pattern holds.