I assume that you are asking for a paradox of the sort that you might use as a hook or attention grabber at the beginning of a paper on the stock market crash. I also assume that you are talking about the “Black Tuesday” stock market crash that helped to bring about the Great Depression in 1929.
If this is correct, I would say that a good paradox would have to do with how it was bad that people were making so much money on the stock market. I imagine that most people would think that it is good for people to make a lot of money buying and selling stocks. However, the fact that people were making so much led to the creation of a bubble that burst on Black Tuesday.
So, my paradox for this would be something like this:
Everyone knows that people get into the stock market so they can make money. Isn’t it odd, then, that the Black Tuesday stock market crash happened because people were making too much money in the market?