Challenge of not having a unified global calendar.
Explanation:
Different nations have different calendars according to their religion and cultures. Each country has its customs to follow with a holiday on that day for celebrations. By having a separate calendar, it creates problems when markets, business, and stock markets are close in a country when the rest of the world is working on that particular day. For tourists, it creates a problem when they are not aware of the national holidays of a country when they find historical sights and museums close. The unified global calendar helps businesses, tourists, and trade.
