We're pretty visual people. It's usually easy to consume data when it's represented graphically as opposed to tabular format. When we're looking at our schedule of activities and events, we typically like to see that information laid out in a standard calendar form.
It's probably fair to say that we all rely on calendars to maintain organization and punctuality. Calendars are ubiquitous; they're on our walls, phones, watches, tablets, computers and even on some fancy new refrigerators. The use of calendars dates as far back as the Bronze Age. Many of the artifacts left by ancient cultures, from rock carvings to monumental structures, were built originally to serve as public calendars. And, since they're an effective timekeeping mechanism, we learned how to read and understand them at an early age.