Applied behavioural economics
I thought carefully about buying a copy of 'Nudge' by Thaler and Sunstein. Apparently, politicians from Barack Obama to George Osborne have been influenced by it, and its ideas are being applied to a wide range of public policy areas. I read the reviews and decided that on balance it wasn't worth buying at the moment, because most of the interesting content was available online and it would be cheaper to wait for it to come out in paperback.
And then I was in Waterstone's, and I saw that it had a picture of big ele-fant and little ele-fant on the front cover.
So I bought it.