When a trendline acts as resistance, it means that a previously drawn trendline—often broken support or a downward-sloping line—prevents price from moving higher. As price approaches this trendline, selling pressure increases, causing repeated rejections, which shows sellers are active at that level. This behavior indicates weak buying strength and confirms that the overall trend is still bearish or corrective. Such resistance trendlines often become good areas to watch for selling opportunities or trend continuation signals.