Why do people play?

Well... mostly for those ''little achievements''. If you play a game, in most cases you are better than you actually are.
Why be a regular guy when you can be a super ultra soldier?

And also, the achievements I said earlier. They are really different. They make you happy.
Killing all the people in the opposing team?
Mining some ores?
Building a farm?
I mean, when you would do that on real life?