The professor fills a mayonnaise jar with golf balls to represent important things like family and health. He then adds pebbles to represent other priorities like work and possessions. Sand fills the remaining space, representing unimportant things. When students say the jar is full, he adds two beers which fit by taking up empty space between items. This shows that while life may seem full, there is always room for socializing with friends. The lesson is to focus on family, health and priorities, and not fill your life only with unimportant "sand", leaving no space for meaningful relationships and leisure activities.