What a gap is
A gap is a jump between the closing price on Friday and the opening price on Sunday or Monday, with no trading in between. Because the market was closed, price did not move continuously — it simply reopened wherever supply and demand put it, which can be well away from Friday's close.
Why gaps happen
News over the weekend — economic, political, or company-specific — changes what people are willing to pay before trading resumes. With no market open to absorb it gradually, the adjustment shows up all at once as a gap when trading reopens.
Why gaps matter for your trades
A stop-loss cannot fill inside a gap because no price traded there; it fills at the reopening price instead, which can be far worse than your stop. The same applies to pending orders. This is how a position can lose much more than the stop distance suggested, and in extreme cases contribute to a negative balance.
How to protect yourself
Consider whether to hold leveraged positions over the weekend at all. Keep size small so a gap is survivable. Use a guaranteed stop where offered, since it honours your level even through a gap for a fee. Avoid over-leverage, which turns a gap into a catastrophe.
Broker's fault or yours?
Gaps are a feature of markets, not broker behaviour. A stop filling at the reopening price after a gap is correct execution. Managing the risk — through size, weekend decisions, and guaranteed stops — is on your side.