Human factors can have a huge impact on the design of systems. Take for example how we choose the food to eat. Two years ago, no one had heard of trans fat. We happily ate oreo cookies and other baked goods oblivious to the damage we were doing to our health.
Then we learned how bad it was for us. But still, it didn't affect our eating because we didn't realize how much of it was in certain foods. So only after the nutrition labels were changed to include trans fat did behavior change. Adding it to the label made the amounts VISIBLE to the user. As soon as it did, there were huge effects. All of a sudden, companies starting making their products with no (or less) trans fat so that people would buy them. We now have trans fat free cookies, cakes, etc.
But we still get lots of trans fat in our foods - because restaurants don't have to have labels, so they can put as much in as they want. And they do. So Americans, Europeans, and most other people continue to get obese in record numbers. If we want to solve the problem, we don't need government to ban trans fat. We value our freedom of choice (trans fat isn't addictive like smoking where we have to be protected). What we need is simply good human factors design. We need the content of the foods we eat to be VISIBLE and then we can make intelligent choices all on our own.