What is the purpose of the mind games in Ender's Game?

We need to remember that in this excellent novel that raise so
many ethical issues, Ender is being prepared in every sense of the word to champion Earth against
the Buggers. As such, the purpose of the mind games he plays, in particular the one with the
giant, are supposed to stretch him mentally, forcing him to think laterally and create different
ways of solving problems that he would never be able to experiment with without the mind games.
We find a very interesting conversation at the beginning of Chapter Seven referring to Ender's
"triumph" over the mind game in killing the giant supporting this
view:

"Isn't it nice
to know that Ender can do the impossible?"

"The player's deaths have
always been sickening, I've always thought the Giant's Drink was teh most perverted part of teh
whole mind game, but going for the eye like that--this is the one we want to put in command of
our fleet?"

"What matters is that he won the game that couldn't be
won."

Thus we can see that the mind
games are all about testing Ender in a different way, a way that forces him to show his
creativity and problem solving skills by looking for extreme solutions, all with the express
purpose of Ender trying to achieve and accomplish the impossible. Just as the mind game couldn't
be won, so the Buggers supposedly can't be defeated.