Pressure causes people to act. If nothing in our lives is compelling us to change, we generally won't. We would do whatever we wanted when we felt like it, and things would be fine. However, there are many pressures placed on people, coming from nature, society, and other individuals.
Colder weather pressures us to find shelter, stay inside longer, and wear thicker clothing. Societal pressure forces us to get jobs to pay for things like food and shelter. And individuals can pressure us to go to places or try activities that we otherwise wouldn't have done.
People often think of pressure as a bad thing. Pressure causes stress and anxiety. People are forced to do things they don't want by "peer pressure". But in reality, pressure is simply a force. It is neither good nor bad; it simply does what it does. People only ever notice when the pressure ends up hurting them.