Put the same chart in front of three traders and ask them to draw the trendline, and you will often get three different lines, each one rotated slightly to fit whatever the trader already believed. That is the honest problem with trendlines: they are the easiest tool on the chart to draw and the easiest to draw dishonestly, adjusted after the fact until the line agrees with the trade someone already wanted.
The two-touch minimum, and why three is better
A trendline needs at least two genuine swing points to exist at all: connect the first two significant lows in an uptrend, or highs in a downtrend, and extend the line forward. Two points make a line. A third touch, price reaching the line later and reacting there without you needing to adjust it, is what makes the line worth trusting. A trendline that required moving after the first extension to keep touching price was never really there, it was a guess dressed up to look like structure, and the market owes it nothing the next time price comes back around.
Angle and timeframe matter
A trendline drawn off a sharp, near vertical spike is fragile almost by design; the angle is too steep for the move to sustain, and the line usually breaks within a few candles regardless of what happens next. A trendline drawn on a daily chart carries more weight than one drawn on a 1 minute chart, because it represents a coarser agreement among far more participants. Match the trendline's timeframe to the trade's intended holding time: a scalp does not need a daily trendline, and a multi hour swing should not be built entirely on a 1 minute line.
Reading the break as information, not doom
A trendline break does not automatically mean the trend has reversed. It often just means the pace of the move has slowed. The more useful signal is what happens to market structure right after the break: does the next bounce still make a higher high, or does it fail and print a lower high instead. The trendline break is a warning to pay attention, not a signal to enter on its own.
Trendlines in ranges versus trends
A trendline drawn inside a genuine trend, where each pullback stays shallow and each push makes real progress, tends to hold up because it reflects a real underlying pace. A trendline drawn across a choppy, directionless stretch, connecting two lows that happened to line up during a period with no real trend behind them, usually breaks the first time it is meaningfully tested, because there was never a consistent pace for the line to represent in the first place. Before trusting any trendline, check whether the broader structure is actually trending, higher highs and higher lows or the reverse, rather than assuming a line is meaningful just because two points happened to connect.
A worked example
Nasdaq's uptrend trendline connects two swing lows at 18,900 and 19,050, extended forward, and a third touch near 19,150 confirms it with a clean bounce. Price later breaks below the trendline at 19,180 on a strong down candle. The bounce that follows only reaches 19,190, a lower high against the prior swing high of 19,240, confirming the structure itself is turning, not just the line. Entry sits short at 19,185 on that failed bounce. The stop goes above the prior high at 19,245, a 60 point risk. On a $10,000 account at 1 percent, $100 divided by 60 points gives roughly 1.6 contracts at $1 a point. The target sits at the prior swing low, 19,050, a 135 point move. Invalidation is a new high above 19,245, which would mean the uptrend's structure never actually broke.