Knowledgeable people are people who are able to know things. This means that they are able to conquer their ignorance. Obviously, you can’t conquer something that fills you with dread whenever you encounter it. So one of the things you often find in very accomplished scientists and scholars is a sanguine attitude about the things they don’t know.
This comes up in my writing instruction when I prepare students for the experience of sitting down to write and discovering, only in that moment, that they don’t know what they’re talking about. They followed the plan. They took a moment at the end of yesterday to decide what to say today; but, when the moment arrived, and they were typing out their key sentence, they realized they had nothing more to say, or nothing, in any case, that they felt comfortable saying to someone who was qualified to tell them that they’re wrong. Now what?
The short answer is to take the planned 18 or 27 minutes of your writing moment and use it to explore the depth and the breadth of your ignorance on the chosen topic. Rewrite the key sentences a few times at greater or lesser levels of generality until the gears click. Or simply write the negation of the same sentence; if you don’t know why the sentence is true, maybe you know why it’s false? Try to imagine specific examples of the general point you’re making, even if you don’t know they are true. And try to imagine precisely the cases that your key sentence seems to exclude, the experiences that would falsify your claim. Here you can imagine actual facts in the world or the opinions of the scholars you had planned to cite. These images are excellent ways to understand what you mean.
Whatever you do, make sure that you write the paragraph you said you would, however imperfect you already know it’s going to be. Later, when the writing is done, you can go looking for the facts or sources that you have vaguely imagined while you were writing. Resolve the issue. Then, next week, write the paragraph properly.