Human beings are fascinated by human beings. This is natural. “People watching” is much more than just an interesting past time. It reveals much about human strengths, frailties, obsessions, drives and motives.
Being intrigued by people is normal. It has advantages and disadvantages. Humans evolved to recognize similarities which enable them to survive in the natural world. They also recognize differences, which unfortunately often serves to make them racist, sexist, or culturally closed.
Watching how others interact, how they appear, how strange or familiar they are, is quite amazing as an educational, activity.
Nevertheless, people watching is a very, very common primate behavior. In our natural state people observe one another, always taking subtle and unconscious clues about human attributes. This data is internalized and often calculated unconsciously.
Human senses allow that other humans spark our visual attention, our auditory attention, our sense of smell, touch, proximity and more. Even how people dress, or what scents they give off is of interest. As human animals, such things as sexuality and aggression are detectable by pheromones, even if human brains do not bring these things to direct awareness.
Some psychologists, and especially Ecopsychologists, acknowledge that humans have at least forty senses. These senses are turned on and tuned in when a person walks in field of view. The person can be quiet or unobtrusive, beautiful of hideous, outrageous or subtle. Either way, human senses pick up and evaluate instantaneously an enormous amount of data.
These days there are so many distractions that the healthy and old fashioned pastime of watching passersby is somewhat lost. People are lost in cell phone conversations, on iPads and smart phones, on video games or tablets. They are often texting, driving, in a hurry or anxious state of disruption. Sometimes, people can be seen multi-tasking and doing all of the above all at once.
Observing this too, is an important aspect of watching others. One can learn a great deal about the artificial buzzing and bleeping world and contrast it to the world in which people evolved to notice things like trees, sunshine, birds and vistas. Seeing people react to nature is enlightening. They often cool down, let down defenses, get calm, or relax in observable ways.
Get out there and do some immersion social experimentation observing others. You will likely learn much about yourself.