If smoking is so expensive why do people do it?

Today is national No Smoking Day and the British Heart Foundation has declared that it will be "pursuing the final fifth" of the UK's population that chooses to smoke.

Their video covers a lot of developments, technological and political, that have seen the rate of smoking decline. But the rate of decline hasn't kept up with the rate of political interventions:

The smoking rate was falling nicely until 2007 when it reached 21 per cent. Since then it has been virtually static, falling by just one percentage point in four years. 2007 saw the start of a new phase in extreme "evidence-based" tobacco control measures, including the smoking ban, the 'fish hook' ads and an increase in the legal age of purchase. Since then it has been open season on smokers, with graphic warnings (2008), a series of particularly large tax increases (2010-11) and a ban on vending machines (2011).

(Velvet Glove, Iron Fist)

The price of smoking has been going up as well. In 1990 a pack of 20 was £1.65. Last March the price of the same pack went up to £7.47 (TMA). This year the No Smoking Day campaign is focused on this cost to smokers, telling them that there are other things they could buy with the money:

It's undoubtedly true that smoking costs often make up a large proportion of a smoker's spending, and many consider it an expensive habit. But that so many choose to keep smoking despite this tells us something: