I think the argument is that political arguments are rarely of the "The sky is blue" category, but more along the lines of (and I'm making up an example here). "The economy has never been better"

There are several ways you could measure this - is it based on the S&P Index? Rising GDP? Income inequality reducing? Low unemployment? Balance of Payments? Not all of those measures may be true at once, and if they're not true which one is the correct measure?

The relative importance could vary from person to person. Somebody with, say, a large pension fund might see the S&P Index as the most important measure. Somebody else might view it as income inequality.

You could argue a case for each one, and each voter would have to make up their own mind as to whether they agree with the statement.