Some things are unmeasurable, at least in a practical, affordable way. David Ogilvy used to say, "We sell. Or else." It's not that all those intermediate steps aren't necessary... they're just not measurable. That's why mapping customer journeys help so much. Figure out the path from attention to engagement to interaction to sale... but don't stop working until you have a measurable sale.
Canalside View: The Trouble with Engagement, 2010-Jun-21 by Martin Weigel
Engagement is one of the most unhelpful pieces of language we bandy around. At best it is entirely meaningless. At worst, it encourages all manner of dangerous assumptions about how people consume communications.
Let’s get specific. What do we need to do for this specific brand, in these specific circumstances, at this specific moment in time, for this specific audience that achieves these specific results? What, specifically, are the triggers and barriers to effecting behavioral change?
We're just fishing...