A failed trendline breakdown occurs when price breaks below a trendline temporarily but fails to sustain below it and quickly moves back above the trendline. This indicates a false bearish signal where selling pressure weakens and buyers regain control. Such setups often trap sellers and lead to short covering, which can push prices sharply higher. A failed breakdown is considered bullish, especially when the recovery above the trendline happens with strong closing and increasing volume, confirming renewed buying interest.