The source of energy that drives air pressure patterns is the sun, because it's heating a second grader at the equator then at the poles, it creates a circulation in the atmosphere. Hot moist air rises over the equator and Flows at the high-level towards the poles, where it cools and sinks. The equator is there for a region of low pressure, and the poles are regions of high-pressure. If something is being "taken off your shoulders" your experience less pressure, whereas if someone's trying to stand on your shoulders, you'll feel more pressure.