This specific writing of CS Lewis, "Bulverism," was very complicated and hard to understand, on the first read. It takes a couple of times to read in order to understand and just scratch the surface of what it is that Lewis is attempting to get at.
Bulverism is a term that is coined by Lewis himself meaning rather than proving that an argument is wrong, a person instead assumes that it is wrong, and then goes on to explain why the other person held that argument. He starts to explain about how everyone's thoughts are "ideologically tainted" at the source, meaning that we think we are right just because of our experiances that we have picked up on in the past, and of all the knowledge that we have obtained in the past. Then later on in the article he continues on by trying to figure out whether or not all of our thoughts are tainted, or just a few.
So he brings up an example of him having a large sum of money in the bank, and that no one can prove that he doesnt just through phsychological examination, they would have to go through all of his posessions that he has in his house and perform the math to prove that he doesnt have that large sum of money in the bank. So he continues on by stating that "you must show that a man is wrong before you start explaining why he is wrong."
This essay makes us really think hard about how we are to think and reason, not only with ourselves but with others, and in order to have a healthy relationship we must logically reason with one another in order to find a better answer.