I now have one simple rule for position management: don't let any single trade affect your sleep.

Holding spot positions is mostly because you didn't think through whether you'd accept a drop when you buy—whether you'll hold on or sell off.
When it rises a bit, you want to cash out; when it drops a bit, you're afraid it will become a big loss.
Futures trading is even more direct—when you're itchy, you want to use leverage to shorten the time, but as soon as the market moves slightly, you're taught a lesson.

Why do I get itchy?
Honestly, it's because I’m afraid of missing out, especially when I see large transfers on-chain or hot and cold wallets moving on exchanges, and everyone in the group is shouting "smart money is coming."
I tend to imagine that if I’m a second late, I’ll miss out on a profit… so I chase in, but with fees + slippage + emotional swings, it usually doesn’t end well.

My current approach is very simple: before placing an order, I write down a sentence—"the maximum loss I can accept and still eat normally."
If it exceeds that, I reduce my position or just don’t trade.
Missing out is fine; after all, arbitrage isn’t as good as sleeping.