Storytime
Barack Obama, during his presidency, wore grey or blue suits almost exclusively. Asked about it in an interview, he gave a simple answer: he had too many decisions to make to waste mental energy choosing what to wear. Steve Jobs had his own version of it: the same black turtleneck, every day. Neither of them was making a fashion statement. They were managing a finite cognitive resource.
Whether decision fatigue is real, in the way the original research described it, is still argued over. The practical observation behind it has held up better than the theory.
The idea, first proposed by psychologist Roy Baumeister and colleagues in 1998, was that self-control and decision-making draw from a limited pool of mental energy, and that pool depletes as the day goes on. Use it up resisting the biscuits in the morning, and you'll have less available when you need to focus in the afternoon. Make fifty small choices before noon, and the fifty-first will be made with less care.
The technical term, ego depletion, ran into some trouble in psychology's replication crisis. Some of the classic studies didn't hold up under re-examination. What survived the scrutiny is narrower. People reliably feel more depleted as a demanding day goes on and drift toward easier options in the evening; whether the quality of their decisions actually falls is still argued over, and a 2025 analysis of millions of clinical decisions found no such pattern. Whether the mechanism is literally a depletable resource, or whether fatigue shifts our motivation and priorities in subtler ways, the outcome is similar. By evening, most people default more readily to easier options: reaching for familiar foods, choosing passive entertainment, skipping the thing they planned to do.
This is directly relevant to habits.
Every time a new behaviour requires you to decide whether to do it ("Should I go for a walk? Maybe I'll do it later. Actually, it's getting dark now. I'll do it tomorrow") you're burning from that cognitive account. The decision itself costs something, separate from the behaviour. And the more your habits live in this zone of daily re-negotiation, the more draining they are to sustain.
This is one of the reasons that genuine automaticity, the point where a behaviour just happens without deliberation, is so valuable. Once a habit is truly automatic, it largely bypasses the decision-making process. You don't decide to brush your teeth in the evening. You just do it. The decision was made a long time ago, thousands of times over, and has since been handed off to a lower-level system in the brain that runs with no real cognitive cost.
What this means in practice: placing your new habit in a period of the day where your decision-making energy is highest, typically earlier, before the accumulation of daily demands, gives it a meaningful structural advantage. Morning habits do form faster in at least one study (Fournier and colleagues, 2017), though the researchers attributed the effect to the morning cortisol peak rather than to spare willpower; either way, the advantage is real.
Environment design plays a similar role. Every time you remove a decision (by laying out your gym clothes the night before, by putting your journal on your pillow, by leaving a glass of water on your bedside table) you reduce friction at the moment that matters most. The choice has already been made, in advance, by a less depleted version of you.
And there's a broader point here that's worth sitting with. The goal of building habits isn't just to do good things more often. It's to move those good things out of the daily negotiation and into the background, so your cognitive energy gets freed up for the things that actually benefit from deliberate thought.
Habits, in a sense, are a delegation strategy. You do the hard work of choosing and repeating a behaviour until it no longer requires choosing. Then you get the energy back.
Bitesized
- People feel more depleted and choose the easier option more readily late in a demanding day, whatever the mechanism turns out to be.
- Every habit that hasn't yet become automatic requires a daily decision to perform it, and that decision has a real cognitive cost.
- Genuine automaticity, the point where a behaviour happens without deliberation, largely removes the cognitive overhead of a habit. Placing new habits in the earlier part of the day gives them a structural advantage before decision fatigue accumulates.
- Environment design (laying things out in advance, removing friction) pre-makes decisions so you don't have to rely on willpower in the moment.
- The deeper goal of habit formation is cognitive freedom: automating good behaviours so your mental energy is available for things that genuinely need it.