A trendline acting as resistance means that in a downtrend, prices repeatedly move up to a falling trendline but fail to cross it and then reverse downward again. This shows strong selling pressure near the trendline, where sellers dominate and buyers lose strength. Each rejection from the trendline confirms it as a resistance zone and indicates that the overall trend is still bearish. A clear breakout above this trendline usually signals a possible trend reversal or short-term bullish momentum.