What a trend line is
A trend line is a straight line drawn along the swing points of a directional move. In an uptrend you connect the rising lows; in a downtrend you connect the falling highs. The line acts as a visual guide to the trend's slope and as a potential area of support or resistance.
Traders watch trend lines because price often reacts near them, respecting the line for a while before eventually breaking through. A break of a well-established trend line can signal that the move is losing steam, though it is far from a certainty.
Drawing them honestly
The danger with trend lines is that, with enough imagination, you can draw a line to support almost any story you want to believe. This is a form of self-deception. A meaningful trend line connects at least two clear swing points and is confirmed by price touching it a third time without you bending it.
Be especially wary of adjusting a line after the fact so that it "worked". A line only tested in hindsight tells you nothing about the future. The value comes from lines drawn before the next move, then honestly evaluated on whether they held.
Using them with discipline
A trend line can help frame a trade — for example, considering entries as price pulls back toward an intact uptrend line, with a stop beyond it. But the line itself does not guarantee a bounce, so it must be paired with a defined stop-loss.
Treat trend lines as one input among several, not as a crystal ball. Markets do not move in straight lines, and no line survives forever. The skill is using them to organise your thinking about risk, not to convince yourself the future is knowable.