Yes, need to use some common sense here, there is scope for some optimization but using common sense discretion and probably not by just finding the exact best parameter value.
This is a very wrong way to think about an edge.
It is important to understand what an edge is.
If a setup fails many times, it does not mean TA does not work. EVERY setup will fail sometimes, we are dealing with probabilities and not certainty. You can have everything absolutely perfectly setup and yet the trade can fail.
So what is an edge ? Simple and obvious. Its = Amount You make in winnning trades - Amount you loose in losing trades - costs.
There are other things you can add to refine what an edge is but above is the most basic idea. You probably know this already but above post made me doubt that so i put it here.
Once we have that then any idea/pattern etc has to be tested on your market for a large number of trades to check whether it actually works. For exampke, Does double bottom/top work ? Define it clearly and then take say 100-200 trades or more and then check - did you make money ? If not then it does not work ( atleast in the way you defined it). Anything that any guru says is irrelevant if it does not test out.The worth of any idea is only to check whether it works, although discretionary parts are hard to replicate and define but we must to do that as best we can in a trading plan.
Some posts you may want to read,
here and
here also check linked posts within it. Or just google Adam H grimes + edge. Even better read his blog in full and also read the first book. ( There is a lot of stuff other than that too, hard to keep up ).
In random data, you will not be able to find anything that makes money over the long term after many trades, but we do have edges in real market data. The pdf linked by Dan is a nice read that speculates why edges might exist in the market and how it can make markets more efficient.
Again this is very wrong. Logical does not mean its real or useful. Anything can sound logical and yet it can be against how market works. The question to ask is whether something works and how well it works and perhaps speculate on why - and not how logical or rational it sounds.
I am not trying to pick on you, just trying to say how i understand things.