Two weeks ago I closed a trade for a profit that covered my whole month. Within an hour I'd opened a position twice my normal size on a setup I'd normally skip.
I lost it. Not the account, just the month. But the sequence was so familiar that I went back through my journal to see how often I'd done the same thing.
Nine times in two years. Every one followed a big win.
Money that doesn't feel like yours
Economists have a name for this: the house money effect. In a 1990 study, Richard Thaler and Eric Johnson offered people a coin-flip bet after they'd just been handed a small windfall. Those who'd won something first took the gamble far more often than people starting from zero. As I remember the numbers, it was around 77% versus 41%.
Same bet. Same odds. The only difference was the feeling that the money was already a gift.
That's mental accounting. Your brain files fresh profit in a separate folder labeled "the market's money," and the rules for that folder are looser. You'd never risk your salary on a hunch. You'll risk Tuesday's winnings on one without blinking.
Why crypto makes it worse
Bitcoin has fallen more than 70% from a peak more than once. It's also gone up several hundred percent in a single year. When wins arrive in big lumps, the lump feels like a different kind of money from your base capital.
And the market never closes. There's no end-of-day moment that forces you to book the win, count it, and walk away. The next setup is always one tap away, and you're sitting there with adrenaline and a green number.
Here's the part that stings. The profit is real. It's in your account. The exchange doesn't track which dollars you "earned" and which you "deposited." Only you do.
What it does to your risk
Say you run 1% risk per trade on a $20,000 account. A good week adds $3,000. If you think of that $3,000 as free, a 5% risk on it feels harmless. That's $150 against your usual $200 risk, so it seems smaller than normal.
But you won't stop at $150. House money logic drifts. After the first oversized trade works, the next one gets bigger. After the first one fails, you tell yourself you're only giving back what you won, and you press to break even.
That second step is the dangerous one. The same bias that made you reckless with gains now makes you reckless trying to get them back.
Look at your own journal for this. Sort your trades by size, then check what came right before the biggest ones. If a large win sits in front of most of them, you've found your own version of this bias. Mine took ten minutes to find.
The fix is boring
You can't talk yourself out of mental accounting. I've tried. Knowing about it didn't stop me from doing it nine times.
What works is making the rule independent of the P&L. Position size comes from current account equity and a fixed risk percentage, calculated before the trade, and it doesn't care whether yesterday was your best day in a year. Write it down. Better still, let a bot do the calculation so there's no moment where "this one's special" can sneak in.
One more habit helps. After an unusually big win, I now take a fixed pause before the next entry. I use 24 hours. It costs me a few setups. It's saved me more than that.
If you want to see what a sizing rule that ignores your mood looks like in practice, the methodology and backtest data are published at v33systematic.com. The point isn't the specific system. It's that the system doesn't know whether you just won.