When you're talking about cheap food, or cheap petrol, you're usually talking about a finite quantity - you can only eat so much, there's only so much fuel you can pump into a tank.
But with cheap drink, a different dynamic comes into play. It has been known, for example, for a person to go out with the firm intention of consuming only a few pints of cheap drink, only to find that the drink, of its very nature, is compelling him to exceed his budget, to squeeze in a few more pints, and maybe a few on top of that.
The 'Welfare Wednesday' initiative at the Liz Delaney pub in Coolock may have had the stated purpose of helping unemployed people to cut down on their alcohol bill for the month, but then in certain convivial circumstances that bill has the potential to rise exponentially - we Irish are a spontaneous people.
Source: Irish Independent, 11/01/2014