they're self-fulfilling prophecies broken by the outside world's messiness.

There is (of course....) no God of the Market that makes things move in some mystical directions. But traders want "rules" so they can trade; if the other traders also believe in these rules, then they act by them, and acting by them makes them come true.

Algorithms need to be trained somehow on how to trade - algorithmic trade happens in milliseconds without human intervention - and then, these humans looking at charts divining things become trading rules algorithms use, thereby strengthening the self-fulfilling prophecy.

But these can only ever be "internal", i.e. they make rules only based on price movement; there is no outside world to these, and in the real world, there is, of course, an outside context problem to movements. These can and do break these rules regularly. They'd only work 100% if a) ALL traders used them all the time and b) market price movement happened in a vaccum without outside context problems.

Yes, Iain Banks reference. ;)