You are certainly right that price can move adversely very quickly. And this is why we need to be very clear which tools are appropriate for which problems…
Any system/method/approach can only do what it is specifically designed to do. And most of the time we only look at trading methods for three purposes: which direction, where to get in, and where to get out. And, as you say, there are thousands of variations of these methods, all of which work some of the time - but not all of the time!
But none of these can resolve the problem that "like with all stocks the bottom can fall out at any time." Why? Because we are using the wrong tool for the job. This is work for our risk/money management tool, not our method tool.
It is a common, and understandable, reaction whenever our method fails, to seek additional indicators or PA techniques to try and “plug the holes” in our method which seem to be suddenly letting in the water and sinking our ship. We will never achieve a totally watertight ship because the sea will always, at times, do the unpredictable. If we knew what that was then it would no longer be unpredictable.
But the good news is, we don’t need to know when or where the unpredictable will occur.
Firstly, we need to understand and accept that what we are trading is “probability”. This means what we are trying to identify is the “likely but not always” nature of where price will go next.
Identifying likely direction is possibly the easiest part of trading. Whereas knowing where to exit a trade is possibly the hardest part of trading. And this is where we need to apply our risk/money management rules.
There are three parts to any price chart:
- where the price has been
- where the price is now
- where will price go next
And we only know parts 1 and 2 which we see looking to the left on our chart. But we cannot know part 3 which is looking to the right on our chart.
So it is therefore easy to realise that whilst our trading method can identify the most probable next direction, it is always only based on extrapolating from parts 1 and 2, whichever method we use. And simply seeking for more variations on the method will not change this basic fact.
The fact that the future is unknown means that we are left with an “if-then” element in our trading decisions. Once our method has given the direction and we enter the trade we also need to know the two “if-then” solutions: If price goes in the right direction then where do we get out? And if price goes in the wrong direction then where do we get out?
This is where we need to remember that our overall consistency in trading is NOT conditional on each, individual trade. Rather, it is the sum result of all our trades over time.
This leads to the need to analyse the success rate of our method in combination with our normal profit size and stoploss size. This is then overlaid with risk analysis of our choice of position size and possibly scaling in and out of positions.
In summary, I guess most methods/systems work some of the time. But whether we can use them to consistently produce a net profit over time is more a function of our risk/money management - and this is the area that is so often neglected. Instead we tend to just move on from one method to another, or look for more indicators and lines and shapes and candles to hook onto our existing method…
Trading is not so difficult once we learn which tools to use for which purpose 
