It’s great advice to evaluate content, but the reality is that it isn’t possible. The reason is pretty simple.
In a complex world, nobody can know even a fraction of the things to be known — a tiny fraction. So, we look elsewhere to learn, to find out something, and so on, but we truly often do not know whether what we are reading is true, partly true (most often the case) or blatantly false.
We have to rely on others, and often that reliance involves a leap of faith, because we cannot accurately evaluate content for its truth value.
Unless it’s something we know as well or better than the entity that produced the content.