There are some good reasons for eating healthy foods. But why bother, people feel just as well whether or not they eat healthy foods. Besides, eating what you like is more pleasurable. Oil reduces friction because a. Molecules are always moving, oil slows down that motion. Slower moving molecules get out of each others way more easily.
Oil keeps moving surfaces separate from each other.
Friction produces heat. Oil provides a route for heat to escape. Lower temperatures means less binding of the surfaces. Oil disolves molecules at the surfaces of materials so they flow out of each others way. Pressure at the knife's cutting edge causes heating of the material.