A trader can end up with a negative balance in MT4 primarily due to high market volatility, insufficient risk management, and the use of leverage. Here’s how:

1. Leverage and Margin Usage: MT4 allows traders to use leverage, amplifying potential profits and losses. If the market moves sharply against a highly leveraged position, losses can exceed the trader’s initial deposit, resulting in a negative balance.

2. Market Gaps: Sudden price gaps, often caused by news events or low liquidity, can lead to significant losses. For example, if a stop-loss order is placed but the market gaps beyond the stop-loss level, the trade may close at a much worse price, potentially driving the account negative.

3. Slippage: In volatile markets, slippage can occur, meaning trades are executed at a price different from the expected level. This can exacerbate losses and push an account into negative territory.

4. Inadequate Risk Management: Failing to use stop-losses, overtrading, or risking too much capital on a single trade increases the risk of severe losses.

5. Lack of Negative Balance Protection: Not all brokers offer negative balance protection, so traders are fully liable for any losses that exceed their account balance.

Proper risk management and choosing brokers with negative balance protection can help mitigate this risk.