Does the sun go down or does the earth come up?
In On Certainty Wittgenstein writes:
80. The truth of my statements is the test of my understanding of these statements.
81. That is to say: if I make certain false statements, it becomes uncertain whether I understand them.
Broadly speaking, this is not correct. For example, when the Inquisition sentenced Galileo, because he denied the official doctrine of the roman catholic church that the earth is the centre of the universe, the inquisitors understood and knew exactly what they were talking about, although their doctrine appeared to be false – and was actually already superseded in those days – and Galileo appeared to be right. What is true is often not a matter of yes or no but it must be seen in the perspective of place and time (history). This is for social facts even more so than for physical facts.
And what to think of lies? They are produced with insight and understanding of what’s true.There are many other instances that speak against the truth of these two combined statements, at least in general.