I think games must present challenges for users to solve. Creators must present a challenge for the users. You want the users to give it all to solve it. And even if they can't solve it they can't help but to want to try it again and again. That is what makes the game interesting. Of course, you can't make things too difficult. You want to give the user the impression that they are close. And even if they make a mistake, it's because of the way they played and not that the game is impossible. This is an important balance to maintain.