Decision fatigue is this phenomenon where the more decisions you make in a day, the worse your decision-making skills become for the rest of that day. It's weird calling it a "phenomenon" because it sounds like common sense, but in our hectic lives, we forget just how big of an impact bad decisions can have on our lives, no matter how small they may seem.
Decision fatigue is why Mark Zuckerberg wears the same t-shirt every day. It's the reason Obama ate the same breakfast every morning as President. It's also why prisoners are 50% more likely to be approved for parole if their session with the judges is in the morning rather than in the afternoon.
It's important to be aware of this fact so that you don't make terrible decisions that you'll have to pay for later. But you should also be mindful of something else: Everyone is affected by this phenomenon. Not just you.
Knowing this, you can start making decisions based on how decision-fatigued other people may be. You can even "weaponize" this knowledge and use it to your advantage. I know this sounds a little sociopathic, but hear me out.
Chess is a game of decisions. Every turn, you have, on average, 30 possible moves that you can choose from. You can ignore most of them because they probably suck, but how do you decide between the 4 or 5 that all look decent? Well, you sit there and think -- 5, 10, even 30 minutes of thinking for a single move. Your brain is going at 100 miles per hour for a single decision. You make your move, and now it's your opponent's turn to overclock their brain and decide between 30 moves. Now, you repeat this process 40 times. These many decisions are going to leave your brain feeling completely fried. The number of serious decisions you have to make in a chess game is mind-boggling. Garry Kasparov once described it as "mental torture."
When doing your calculations for a move, players often try to make the move that will be best for them, which makes a lot of sense. You want to move the needle ever so slightly in your favor. But as you get better at chess, you need to factor in how your opponent will react to certain moves. If you make things simple for him, the number of decisions he'll have to make will be few and relatively simple. However, if you start introducing complexity simply to screw with your opponent's mind and force him to think: congratulations, you've just weaponized decision fatigue.
The current world chess champion, Magnus Carlsen, is a master of this concept. His ability to weaponize decision fatigue is one of the reasons that his opponent for the 2021 FIDE World Championship, Ian Nepomniachtchi (one of the best chess players alive), basically hung an entire bishop on the 27th move of the 9th game.
No one is safe.
When you become aware that everyone is affected by decision fatigue, you can start doing simple things that will have a positive impact on your life. Some ideas:
See, that wasn't so bad. You probably thought I would write about using this concept to take down your enemies. You can get pretty selfish and sociopathic with it, but that's not the goal here. "Mentally torturing" my chess opponents is the furthest I'm personally willing to take it.
The main message is to not forget that decision fatigue affects other people. Yes, you can wear the same t-shirt, eat the same breakfast, and follow the same routine every day to cut down on your own decisions, but, ultimately, we live in a society where other people's opinions and judgments will affect us. It's essential to be aware of it to avoid getting screwed by other peoples' decisions simply because it's 5 PM and they're tired.