The main thesis if this small book is that we can best achieve our broad life goals --- from personal happiness, to a company maximising shareholder value --- indirectly. Kay gives examples of companies that prosper when their aims are "to be the best in X", yet crash and burn as they change their aim to "maximise value".
Despite the subtitle, there's not a lot of explanation of why this is so, beyond that the world is too complex for us to know how to achieve goals directly. I suspect it also has something to do with the high level goals being much too vague: how does "maximise value" convert to actual behaviours?
Some of the early material feels a bit like padding, but there is some more substance towards the end, with suggesting for how to be fruitfully oblique. It is a good way to pass the time on a long train journey.