trendline is simply the result of the collective sentiment. If you compress all the candle bars the trend lines cross. you will get something like this. it tells you at which point, the collective result from every trades stops going lower then reverse. You could imagine it as a market place slowly gets more and more crowded. there're people leaving and coming all the time. Each of them has mind of its own(like a trading bot or person who follows one's own logic to participate). Since each bot would stick with the same algo. without switching to a completely different set of algo. its action would be somehow linear. without sudden change of environment(bus full of people dropped off, terrorist attack etc.) It should more or less come up with the result like the trend line.
I wouldn't consider this evidence that they work. 20/20 Hindsight ... Cherry picking ... etc. Evidence would be showing them working in real time, a video of someone trading with them (even if it's just sim trading, or just making real time calls) for example.
In this chart, trend was down, price then pulled back up then started to fall. Using R and S lines we see price within a range that is wide enough to trade. Trade setups were made short with overall current trend near top of range targeting bottom of range for scalp trades. Risk was reasonable vs reward.
Trendline itself is not a strategy, you need to combine it with other signals for better evaluation of its effectiveness.
It's just something I figured out while staring at the monitor drooling. The most important realization for me is that the market isn't 5 or 10 major participants but a huge collection of entities. We are simply seeing the end result of a collective movement. So to switch to a different mind set would probably help you to look/use the tools with a different approach. I guess it could be called DICK, displacement in candlestick
"Tradeline" instead of trendlines, and "fastesr" instead of fastest, let me guess, 4th Heineken? Trendlines work in any time frame (that includes day-trading on the 5 or 15 min charts), if you know how to deal with the false breakouts and the phony "pullbacks".