Risk a fixed % of your account on every trade.
Professional traders typically risk 0.5–2% of account equity per trade. At 1% risk with a $25,000 account, the maximum loss per trade is $250. This allows a 100-trade losing streak before full account loss — a statistical impossibility with any edge.
Position size = (Account × Risk%) ÷ (Entry − Stop Loss). Never size based on a "round lot" — size based on your predefined risk.