You can still lose money with a stop-loss because the order limits risk without eliminating it. It only helps limit risk; it isn't foolproof, with market price gaps, slippage, or sudden volatility causing your position to close at a current market price that is worse than expected.
Setting the stop-loss too close may lead to the market triggering it prematurely, cutting off potentially profitable stock, commodity, forex, or option trades.
Treat it as a safeguard, not a guarantee, and combine it with proper position sizing, realistic placement based on volatility, and awareness that gap risk increases overnight or through earnings.