I agree (of course).
But much more usually, when aspiring traders try to use an additional indicator to "confirm" something, they're using it as a filter to reduce their entries hoping that a higher win-rate will make for a more profitable system, and of course it usually doesn't. Their perspective on this subject typically - albeit not always - arises from a confusion (through no fault of their own at all), on some level, between "entry methods" and "trading systems".
The problem, in the context of this thread, is that to be able to identify confidently the times that doing that actually does increase profitability (even assuming sufficient understanding of indicators as to be able to do so!), requires a skill-set not normally available to the people who want to try to "confirm something with an indicator" as a short-cut. In my experience.

