By "interpretation" am I correct in that you are referring specifically to subjectivity? If so, isn't what we take to be subjective simply that which we have no natural nor conventional definition established by which to judge that which we seek to understand through subjective interpretation?
I see price bars as objective as a moving average. I do not agree with those who disparage indicators because they are "derivitive" because the fact is that price bars themselves are derivative. The only non-derivative feature of price action available to us is, at best, the current bid-offer spread. Even the tick, the most recent individual transaction, is derivative.
These are all important questions that must be defined by the trader in advance. Differentiation is a matter of definition, some would add, quantification.
A different question would be "how do you know it is a reversal and not a pullback?" You know because you will have defined each, and at some point the price action is going to move in a manner that disqualifies it as a pullback and instead characterizes it as a reversal, or it is going to move in a manner that confirms it was a pullback. There is, of course, no way of knowing before hand which is going to occur. There are, however, ways to determine which is more likely, and an optimal moment to take a position, place an exit stop loss in case price doesn't confirm, profit capture and target taking, etc.
I think the high failure rate has much to do with the unwillingness of most to study their chosen market, learn its character and behavior, and formulate a trading plan that will allow them to capitalize on the understanding of market behavior they developed.
I also think pattern recognition is important, and the ability to recognize such patterns in real time is very rare. It is made even more difficult by the fact that most humans think they are smarter than they are and even smarter than the rest of humanity. That is why they will continually lose shorting a market day after day after day because they "know" the economy is piss poor and this things going down only an idiot would be long here based on the most recent date we have on Peking duck imports.