A great UX is designed around how people think.
1. Limit the amount of options a user has
2. Don’t force users to do something, but suggest them instead
3. Users copy the behavior of other users, so use social proof to steer behavior
4. Users value something more if it is scarce
5. Users want to stay consistent with their past behavior
Did you spot the least ethical UX? It was the one on social proof. This UX steers an uneducated user towards a purchase that might not be best for her/him, while the other examples reduce mental effort for the user in a less intrusive way. These are just a few examples to explain how knowledge of behavioral economics is key to UX design.