How Much Planning Goes Into Your Gameplay?

I've tried planning a couple of times, but I always get bored before I'm even done with the setup. Mostly I just let the game and/or my characters decide what happens. I had a couple who seemed to be really happily married for a long time, so they decided to have a child. The game gave them triplets. One of the triplets ended up spending a lot of time with the dog when everyone else was doing other stuff, so that child ended up focusing on animals and eventually became a veterinarian. When I first created the couple, I certainly didn't plan for them to have a veterinarian child. In fact, originally I didn't even plan for them to become a couple. After they had those triplets, I figured the couple wouldn't have any more children, but then the father got abducted by aliens and had alien twins. No empty nest syndrome for this couple! They still have two alien toddlers running around!

I only have my characters do what I think they would actually do. I'm dying to play in the Realm of Magic, but it hasn't seemed right yet. I have a couple of characters in mind who I would love to have become spellcasters, but it just hasn't seemed right yet.