What methods go in the model vs. the controller?

I suspect my brain is staring to reform itself to Rails thinking, but
I need help with a concept:

On p. 150 of the Agile Web Dev book, we put a method in the Orders
model: add_lineitems_to_cart.

Why did this go in the Orders model instead of the Store controller
(where we were just saving the cart to the database)?

Thanks,

Hi Austin,

Check out this article by Jamis Buck, I think he explains it well why
it's better to have models pulling as much of their weight as they
can.

http://weblog.jamisbuck.org/2006/10/18/skinny-controller-fat-model

Tim Case