Shaken? If by that you mean a book that was so clearly well done as to make me question my politics, relationships and hope in humanity, I'm gonna have to go with The Uses of Pessimism by Roger Scruton.

One of the greatest things the book provides, in my opinion, is some very powerful concepts that allows you to be direct with people without personal affront. For example, I was working with some non-developers on a project for a competition but we were unable to get the data that we needed; when I was asked quite directly whether or not we should abandon the project, I told him "Continuing with this would be unscrupulous optimism." There is no reason to simply hope that we'd get the data we needed in less than 20 hours (it was for a contest). It would be a waste of my time, theirs, and stress + painful, and an end product that I critically think would just end up as a load of fear-mongering, hence unscrupulous.

Now the funny thing is this book was in part funded by a conservative think tank. Needless to say, it's not within the range of my usual reading. However, it has made me think a lot more conservatively, so I guess that counts.