The BBC science programme Horizon has just broadcast a fascinating episode which looks at human subconscious bias and how our thinking is made up from two very different parts of our minds. Much of our decision making is determined by which of the two parts gets used – the fast, quick Part 1 (intuition) or the slower, more thoughtful Part 2 (logic). Where these two come in to conflict some very odd things happen.

Of concern is that the same bias and traits are shown by monkeys who diverged from human several hundred million years ago, so we may not be able to unlearn them.

The programme shows how the current financial crisis was brought about by how humans react to gambling, where we most often ‘double down’ when losing but get cautious when winning.

If you can watch it, it is here for the next six days.

Oh, and the question in the title – it’s because cab drivers have in their minds a fixed amount they must take in fares each day. Once that’s done they call it a day. Because, on rainy days they earn more quickly, they knock off earlier. On summer days they drive for longer to make this same fixed amount.