A game must have some objective one is supposed to accomplish. It might be an overall goal that finishes the game when it is accomplished, or it might be an ongoing objective being accomplished again and again.
The stated objective in the game is never the real reason for the game. The goal itself is somewhat arbitrary and might have no value outside the game. What is important about a soccer game is not that the ball gets into the net of the goal. It is the excitement derived from playing or watching the game that is the real reason behind doing it.
Likewise, the challenges and obstacles in a game are not the real challenges, but have been chosen deliberately in order to make an interesting game. The players in a soccer match might get along great in the locker room or when they are having a beer afterwards, but during the match they are divided into two opposing teams that try to wipe each other out.
A good game has a fairly even balance between freedoms and obstacles. The freedoms are all the things one can do to play the game and all the choices one has. A game is probably most fun if there are just a few more freedoms than there are obstacles, so that one can do well in the game despite the risk of being stopped.
A game has some kind of rules. Actually they are simply a description of the freedoms and limitations in the game.
A limited game has fixed rules and usually there will be winners and possibly losers in the game. In an unlimited game the rules change as one goes along to always maximize the fun of the game. In an unlimited game there usually aren't any losers.
Tennis, soccer, sweepstakes, the stock market, court cases and crossword puzzles are all limited games.
Playing with Lego bricks, dancing, writing a book, starting a company, figuring out life or improving oneself are all unlimited games.
The advantage of making a game out of something is that an element of surprise, and thereby learning, is added. We make something about the whole activity unknown. It can be very attractive for people to find out what surprises are hidden in a game, through making the unknown parts known.
A game includes the lie that one doesn't already have the goal of the game. One agrees that one is being kept from achieving the objective and one has to do something to get to it.
If you want people to read books, it works best if you get them to agree that there is something in the books that they don't know, but that they would like to find out. Then people will happily work hard at reading the books to learn something. If they thought that they knew everything, they wouldn't bother to read books.
The maker of a game might or might not admit the lies that the game is based on. If she keeps the lies a secret, the game might become aberrative. People might take it too seriously and might believe that they really HAVE to play the game, and the goal is REALLY important.
People love playing games. The fun and learning achieved from playing can motivate them to deliver their utmost performance and work hard for the game. They usually don't mind much that they are being tricked a little bit into playing the game. Often games designed by others can be most fun because you can't quite see through all the mechanics of the game. That can allow you to just experience and enjoy the game without a danger of accidentally undoing it because you know too much about it.
If you design a game for others to play, make sure that you don't make the real purpose of the game the stated goal. If you want to make a game to have fun, then don't make FUN the end goal. Then the players would have to agree that they aren't having fun before they could play the game. That would not be a good idea. If instead you select something fairly unimportant as the goal, the players could have fun all the time while pursuing it.
If you make a game with the purpose of giving people increased abilities, don't make the abilities the stated goals of the game. Then the players wouldn't be able to have those abilities before they had finished the game. That would be a shame. Rather make a game with tests and challenges that are going to require the desired abilities to be demonstrated in order to overcome them. That would encourage the players to have the abilities without entering into any agreements about not having them.