It's volatility. How do you flip a coin and sometimes you get 4 heads in a row? That is why statistical data is based on large samples. You will also run into periods where the payouts are small. Remember, with these "multiplier" machines, when you hit something big, its big. If you had a machine with no multipliers, you would see the pays even throughout the cycle and your bankroll would last longer. But according to focus group studies, they say that players today would prefer the HUGE pay once in while, than a series of smaller pays but more often. So now we have extremes, where you have machines that hardly ever pay (you can go through $100 on a penny machine within minutes). There will be that one time in a long while, where you will hit something big. Machines have been trending to the big win since the mid 90's when the 10x pay type machines started to appear. The original video slots where a lot less volatile, but they didn't have the HUGE jackpots until the second generation came about and players where more apt to playing $2 to $3 a spin on a "penny" machine. The original video slots where like 9 lines and 5 credits per line bet max, that's a 45 cent max bet. Nowadays, you rarely run into a machine that has a minimum bet of less than 40 cents on a minimum bet.