The rule before this one told you never to trade after drinking, because alcohol installs the "I don't care" attitude that empties accounts. Rule No. 13 is its quiet twin, and in some ways the more dangerous of the two — because fatigue does almost exactly the same thing to your mind as alcohol, except you never chose to pour it, and so you rarely notice it happening.
This is not a metaphor. Research into fatigue and performance has found something striking: stay awake long enough and your cognitive impairment becomes comparable to being legally drunk. After enough hours without proper rest, a person's judgement, reaction time and decision-making degrade to roughly the level of someone over the drink-driving limit. So when Felix says tiredness brings on "the same as alcohol," he means it almost literally. The tired trader is, in measurable terms, an impaired trader — and impaired traders lose. The rule is therefore as firm as the last one: never trade when you're tired.
The morning: trade rested, or don't trade
Begin with the start of your day, because the day is often lost before it begins. You sit down to trade in the morning, but you slept badly, or too little, and you are tired. The temptation is to push through — coffee, screen, get to work. Resist it. If you are not properly rested, you should not yet be trading.
A tired mind in the morning makes the same class of errors a drunk one does: it misjudges risk, it reacts slowly, it reaches for shortcuts, it lets emotion run where discipline should be. Every rule in this series depends on clear cognition, and a sleep-deprived brain simply cannot supply it. The good news is that you are never obliged to be in the market — a theme that runs through these rules from patience (No. 7) to the junkie's compulsion (No. 11). There is no rule that says you must trade today, this morning, this hour. If you are tired, the disciplined move is to wait: rest, recover, let your head clear, and come to the market only when you are sharp. A missed morning costs you nothing. A morning traded half-asleep can cost you a great deal.
The evening: know when you've had enough
The other end of the day is where fatigue does its most reliable damage, because trading is genuinely exhausting in a way outsiders never appreciate. Hours of sustained concentration, constant decisions under pressure, the steady drip of adrenaline — it drains you far faster than its physical stillness suggests. And the modern trader can stay at it a long time: the American markets run late into the European evening, to ten or eleven at night, and the screen will happily keep you there.
So picture yourself deep into a session. You started in the morning and you've now been at the screen well over eight hours. You don't feel dramatically tired, but the edge has gone — your focus is fraying, you're a half-beat slower, and that familiar, fatal looseness is creeping in. This is the exact moment the "I don't care" attitude from Rule No. 12 arrives, only this time it's exhaustion pouring the drink. You stop concentrating properly. You take a trade you wouldn't have taken fresh. You manage a losing position lazily because you're too tired to do it right and a part of you just wants it to be over.
The discipline here is to know your limit and honour it before you reach it. After a long session, recognise that your best decisions are behind you and the quality of your trading is now falling, regardless of how the markets look. The professional move is to stop — to close the platform while you're still sharp enough to make the decision to close it, rather than trading on into the fatigue until it makes a worse decision for you. The market does not reward endurance. It rewards good decisions, and good decisions have a shelf life that runs out long before the trading day does.
The athlete's lesson: don't eat your brain into a coma
Here is where trading and endurance sport turn out to be the same discipline, and it's a lesson every serious athlete knows in his body.
Ask any distance runner what happens if he eats a big meal before a race. He slows to a crawl. The reason is simple physiology: when you eat a large meal, your body diverts a great deal of blood to the stomach and digestive system to process it. That blood has to come from somewhere, and what it is taken from is, in effect, the rest of you — including, crucially, the brain. The athlete feels it as heavy legs and a foggy head; he cannot run fast on a full stomach because his body is busy digesting instead of performing. This is why no serious runner races on a big meal, and why the heavy, drowsy feeling after a large lunch has a name — the "food coma" is real, and it is your blood and energy being pulled toward digestion and away from your mind.
Now apply it to the screen. Trading is not a physical performance; it is a cognitive one. Your brain is the muscle you are asking to perform, and a brain short of blood and energy is a brain that thinks slowly and decides badly. Sit down to trade after a big breakfast, a large pizza at lunch, a heavy meal at the Chinese restaurant — and you have done to your trading brain exactly what the runner avoids doing to his legs. You will feel the fog, your concentration will dull, and you will trade worse, every time, for an hour or more after the meal. You have voluntarily impaired the only instrument you trade with.
So the practical advice is the athlete's advice: stay light while you work. Don't load up on heavy meals during your trading hours. Eat small, light portions, spread out — graze through the session rather than sitting down to a single big meal that knocks you flat. Keep your blood where you need it, which is in your head, and keep your mind quick. A trader who eats like a man about to run a race will think like one too.
Treat your mind the way an athlete treats his body
Pull the threads together and the principle is clear: trading is a performance activity, exactly as Rule No. 1 said at the very start of this series, and your mind is the athlete. An athlete who shows up to compete exhausted, under-slept, or bloated from a heavy meal will lose to a rested, well-fuelled rival every time — and it makes no difference how talented he is. The same is true for you. All the skill and all the rules in the world cannot be executed by a brain that is too tired or too sluggish to run them.
So you manage your mind as deliberately as an athlete manages his body. You sleep properly before you compete. You don't compete when you're depleted. You fuel lightly so your head stays clear. And you recognise when the performance is over for the day and you stop, rather than grinding on into the fatigue. This is not softness; it is exactly how professionals in every demanding field protect the one asset their whole livelihood depends on.
The bottom line
Never trade when you're tired. Fatigue impairs your mind in much the same way alcohol does — research finds enough hours awake leaves you as compromised as a drunk — and it brings the same "I don't care" looseness, the same collapse of concentration, with none of the warning. So trade only when you're rested: if you slept badly, wait, because you are never required to be in the market. Know your limit in a long session and stop while you're still sharp enough to choose to stop. And fuel like an athlete, not like a tourist at a buffet — small and light, so the blood and energy your brain needs to think aren't busy digesting a pizza.
Your mind is the only instrument you trade with. Show up rested, fuel it lightly, and put it away before it's worn out. Trade tired, and you've impaired the one thing you can't afford to lose.