Suddenly saw the dumping, immediately performed a stop loss operation. Looking back now, the reaction was quite quick, but it exposed a problem.

The stop loss order should have been placed at 4. According to the market, the market maker piled up a large number of long positions at 4.2, and it would be dangerous once it fell below 4. But at that time, I didn't set a liquidation price, so I didn't place the order in advance, and ended up manually closing it at 3.5. In other words, the profits from the previous accumulated long positions were wasted.

The lesson is clear—key support levels must have stop loss logic planned in advance; one cannot abandon the stop loss plan simply because a liquidation price was not set. Next time encountering a similar pattern of a dealer stacking orders, such integer levels like 4 must be defended properly; otherwise, if it drops, one will be passive.