Economist Daniel Kahneman at his most accessible (not particularly) and relevant (very). You can also watch it.
“people rely on a limited number of heuristic principles which reduce the complex tasks of assessing probabilities and predicting values to simpler judgemental operations. In general, these heuristics are quite useful, but sometimes they lead to severe and systematic errors.” Tversky & Kahneman, 1974: 1124
If you prefer your behavioural economics a little less dry, you could try instead, Dan Ariely’s book, Predictably Irrational – apparently there’s an expanded edition coming out in May, but I suspect that as a behavioural economist he’s pulling a fast one on us. “Expanded? Must be even better!!”