So here you are, out of game lives again. Which recharge at the rate of one per half-hour. So basically, you have to wait for a while before making another attempt -- or you could just pay ninety-nine cents for an instant fill-up.Here's an impossible level, or nearly so. The initial pattern is random and if it isn't just the right kind of lottery draw, you'll be playing over and over until you get the starting combo which would let you advance at all -- or you can start the game with a powerup which will make the whole thing into a one-shot deal. Only ninety-nine cents.
You just reached the end of the level set -- no, there's more ahead. Only they won't let you play them unless you pass three challenges. And you can only pass one challenge each day: the game will force you to wait twenty-four hours before launching a new one. And this will happen at the end of each set -- or it's only ninety-nine cents to avoid the wait...
You can play the game for free, right? It's a free download. It's a free install. Financially, playing costs nothing.
http://tvtropes.org/pmwiki/pmwiki.php/Main/BribingYourWayToVictory
Winning, on the other hand...
...all those ninety-nine cent purchases do keep adding up...
A lot of games use this model. A lot of games.