[quietbritishjim]

It sounds like you have read the question as "if a person could only read a single book in their whole life, what should it be?"

But I think the question actually meant: "for actual real life people here on HN, who have all probably read some books already, what extra book would you suggest reading?"

For us adults, there are probably books that would have more value than Dr Zeuss, excellent though it may be.