Calendars have been developed over centuries in order to better understand natural cicles and design life inline with the natural patterns.
It is a great example of 'Observe and interact'. During the development of human cultures, societies have developed calenders that make life easier to manage and understand.
Cultures created holidays to celebrate harvest, to celebrate the light in the darkest phase of the year. When farmers observed the passing of seasons and made adjustments and improvements to gain higher yeld and better prepare their soils, their livestock and house.