One reason Hay Day is so effective is that is had a ton of great feedback loops. Completing the loops gives you some reward, and you always have the option to purchase the reward instead of waiting for it. This is true for nearly every possible action that requires time (you can wait for the bread to be made, or you can speed up the process by using crystals).
By feedback loop I mean this:
- The player performs an action
- An outcome occurs based on the action
- The game is updated based on the outcome
- The loop returns with some result
- Optionally, the player could start another loop.
People want to close loops. That's essentially what games are all about: closing loops. Level your character, get new gear so you can reach the next level to get better gear...close one loop to start another. Rinse, repeat. Different experiences, but at the core it's about starting and finishing loops.
A concrete example:
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You click the 'make bread' icon at the bakery
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The game checks sees you have enough materials, so it allows the process to begin
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The process begins. You immediately loss the required materials. However, time is required to get the bread
Now, there's a delay, because you have to wait for n minutes before the loop is closed - before you get your bread.
** WAITING ** -
After n minutes have passed, the game is updated and the bread is finished.
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This is a sort of miniloop now - you collect the bread, and it updates the materials in your barn. Now, you can start another loop and make more bread.
Did you catch that? The loop was opened, but those sneaky bastards won't let you close it! Well, you can close it by waiting for the timer to expire. You don't need to buy anything to play HayDay.
Oh, but how nice of them - they allow you to close the loop immediately by using crystals, which you can easily purchase right in the same window!
Now, check this out. You get a bunch of crystals when you start the game. At the beginning, you see you the timer but you also see you have a bunch of crystals - the game explicitly encourages you to use the crystals to immediately close the loop and get the reward. Later, when you run out of crystals, you know that you could skip waiting because you've been trained to do it.
Let me beat a dead horse now. You want to close loops. Feels good. To close loops in HayDay, you have to wait...or, you can pay money to skip the time delay. HayDay messes with your brain. You can immediately close loops when you start, but you have to buy more crystals later to immediately close them.
It's not pay to win and you don't feel cheated if you don't buy crystals - you still have to harvest, to build, etc. You're basically just paying to allow yourself to immediately close loops.