A story from about a year ago, when Junior was 4, that illustrates this idea. I was asking him to do something, such as putting on his shoes. He refused, preferring to play.
Me: Junior, I want you to put on your shoes.Junior: Well, you don't always get what you want. (Something I had told him earlier.)Me: But it is a mitzvah of kibud av va`em to listen to me.Junior: Even Hashem doesn't always get what He wants!Me: What do you mean?Junior: Well, Hashem wants me to do the mitzvah of kibbud av vaEm, and I am not doing it. And so Hashem isn't getting what He wants!
This naturally led to a discussion of bechira chofshis, and that what Hashem wants is for us to have the ability to choose to not do what He wants, because that way it actually means something when we choose to follow God's will. Otherwise, we would be robots, or malachim.