It is the nature of the volatility of the slot. The 89% holdback is a number derived on a lab simulation of MILLIONS of games played. In the short term, you will have volatility swings depending on the game. I will work out in the long run. If you are running a casino, it's part of the business. Some slots will have negative returns in the short term, but over a long period of time, it will balance out. You will rarely be at 89% in the short term, if it is smack 89%, then it wouldn't be considered a random event if the payout was fixed all the time.