The thing that confused me about Random Walk down wall street was that he spends the whole book explaining that all strategies for investing are useless, and then in the last chapter he gives out advice for investing.
I think he included that because some people just won't listen and they really really want to pick stocks instead of invest in index funds. I think he had to acknowledge that those people exist, but try to mitigate that desire by writing the first 400 pages about sensible investing.