In practice
A clean trendline with several touches teaches traders to buy each touch and place stops just under the line. The cleaner the line, the more orders build up beneath it.
Traders who think in liquidity treat such a line as a target: they expect price to break it eventually, run the stops below, and only then show its real direction.
What to watch for
A trendline can hold for many more touches than expected, so shorting simply because the line will break one day is no plan. Wait for the break and for what price does after it.