Lots of Noise
One of the biggest ways that slot machines will trick you into staying on them for an extended period of time is to make lots of noises, whether you win or lose. These noises are typically high pitched and exciting. Even the noises that are emitted when you lose still have a hint of excitement in them, and this will often make the loss feel less frustrating. These noises keep the game interesting and keep you playing them in hopes that you'll win, ringing an even more enjoyable sound.
Nobody likes to lose, but people love to win -- even if they have to settle for a close call. The owner of the slot machine doesn't have to pay out if you almost win, and so by offering you close calls they will keep you invested in the game without actually paying anything. Slot machine games will constantly give players near wins as a way to keep it exciting and interesting, and then will throw you a win every once in awhile to keep your spirits up.
Break Even Wins
One of the biggest tricks slot machines use is to have you win, but you not actually earn any money. This is done by making the most common win just a refund of the exact amount that you spent. It keeps you invested in the game because you finally won something, but once again, the owner of the machine is still not losing any money over it. They aren't making money from that particular roll, but they know that the user is going to continue playing because now they are excited over the past results. They will throw you a bone every once in awhile, but look before you bite, for it might be attached to a string.
Illusion of Control
Everyone likes to feel in control of their own money and wagers, and so it's no wonder that slot machines work to make the user feel like they are controlling the outcome. The game will appear as if you have complete control over everything that's going on, when you actually barely have any influence at all and the roll is predetermined for you to either win or lose.
Unknown Amount of Loses
Slot machines try to make it impossible to tell how much you've won, and how much you've lost. You will never see a starting amount and current amount feature on a slot machine because they want you to feel like you're winning. A study was conducted that gave 28 wins out of every 200 games. The players were all asked afterwards how many times they felt they lost, and each one underestimated their loss count. In fact, most of them weren't even close and felt that they had won a lot more than they actually did. This shows just how clever these machines are.
Slot machines are also designed to be addictive to the player. They are very flashy, loud, and have cool animations. This keeps the player on the machine for a lot longer than if it were a boring game, increasing the chances that the owner will make money off them. It's all fun and games until someone loses a paycheck.