Leann Birch, a developmental psychologist at Penn State University, ran an experiment in which she took a large group of kids and fed them a big lunch. Then she turned them loose in a room with lots of junk food.

"What we see is that some kids eat almost nothing," she said. "But other kids really chow down, and one of the things that predicts how much they eat is the extent to which parents have restricted their access to high-fat, high-sugar food in the past: the more the kids have been restricted, the more they eat."

Birch's study also discovered one reason this happened: the children on restricted diets believed the junk food tasted good primarily because they had been told that junk food was bad for them!

This illustrates Paul's insight that the law arouses in us sinful desires (Romans 7:5). It's not only that we break the law because it's trying to control our sinful natures; we convince ourselves that it's really a lot of fun, that it really tastes good—even when it's making us more spiritually unhealthy, and may even be killing us.