Its not their perception of what "it ought to be" though, its their perception of what is. That perception may be true it may not. But even if it isnt true its equally as important as it effects the truth.
How people perceive the economy, particularly over long periods of time, effect how they spend and invest, and that has very real quantifiable long term results.
You simply cant seperate one from the other, which is why the stock markets value is a very critical metric and neccesary (among many factors) in assessing both the current situation but more importantly what the economy will look like in the future.