You are new to casinos, but have been told, quite correctly, that roulette is best game for mug punters. Also you realise that the house advantage is about 3% if you bet on numbers. So you decide that each time you enter the casino, you will bring with you £100. Surely then, the cost of your entertainments should average out at £3?

After a period of time, you will find that it comes to something more like £20. This is because of the constant churning of the money. Let us suppose you bet £20 on each spin and have 40 such bets. Then, you have actually wagered £800. Your expected loss has become £24.

The casino expects to take about 20% of the drop. This is the amount of money the punters change into chips. If everybody walked into a casino, plonked £100 on the table and walked out after one spin, win or lose, the casino would rapidly go out of business.