Risk management
Position size, drawdowns, correlation and fixed risk per trade.
Position size is calculated from the risk: size = risk amount / distance from the entry to the stop.
Losses and recoveries are not symmetrical: after −50% you need +100% to get back.
A common practice is to risk a small fixed percentage of capital per trade (often 0.5–2%), so that a losing streak does not wipe out the account.