Game difficulty

I like a good game and the changes one brings.  There are plenty of solitaire games that one can play that that brings a level of challenge but not to the level of being frustrating.  Regular solitaire, spider solitaire, mahjong, free cell are a few.  Those games use tiles or cards and have endured for many years not only because they are easy to learn and can be played by one person. but because even though the layout of the cards is entirely random one's chances of winning can be  improved as ones skill level improves.
    There are other games that are also fun like cookie jam and candy crush saga that can only be played on a computer.  While those games are fun each section gets progressively harder until one gets to the point of not being able to win unless enhancers are introduced.  These objects can be won but the game makers really want the players to purchase them.  If one choses not to purchase these enhancers certain levels cannot be won without a great deal of effort.  I have noticed that after persistent effort even the most difficult level can be won because the game will suddenly give opportunities it didn't previously.  I like winning but it's like the game creators feel sorry for you and decide to give you a change to win.  
 All levels of Free Cell can be won except for one.  Some games are easy while some seem to be impossible.  Each game is independent of every other game and the next game does not get harder than the one just played, at least not by design.  And one doesn't have to win the current game in order to play a different layout.  I suppose that is what has led these game to be popular as well as enduring.
  I do think that the designer who can make a computer generated game with a random difficult level  which is challenging and fun  will have an enduring and loyal following.  These other games will only keep people playing as long as they can continue to move forward without costing them a lot of money.