Have you ever thought about what this quote might mean? It sounds strange, but I do believe that an educated person should be able to debate with himself, or debate with others... also presenting facts and defending a case that the person doesn't necessarily agree with.
That is what I believe the quote is about. You should be able to see a case from different perspectives, and thus you should be able to entertain yourself with thoughts on a matter, and also thoughts that you do not agree with. But, you might have a goal to try to understand them and as you see the case from a different perspective, you might not agree, but you can see where the arguments of other people come from.
This will not only make you better at understanding, but you will even be able to protect your own point of view in a greater way, because you have actually done a deep dive into the thoughts of everyone else.
This might be a bit deep, but I do find it to be an amusing and interesting quote from Aristotle.