There are things that we take for granted, which is reasonable given that there are a whole lot of other things that we have to think about, so these things on the mental wallpaper are simply assumed to be (when the decoration is first applied it draws attention, but soon it simply blends into the background).
Take, for example, the calendar.
Prior to the period when Quintus Fulvius Nobilior was running things in Rome—153 BCE—the calendar had ten months, not 12.
The last month of the year, then as now, was December. And the month got that name from Latin, decem, or ten.
But the Roman senate, perhaps being more scientifically capable and knowledgeable than those who currently have offices in the U.S. Capitol, decided that it would be better to have a calendar that was more aligned with what was happening in the heavens, as it were: the lunar cycle—the time it takes the Moon to go through all of its phases (i.e., from new to new)—lasts 29.5 days. And a solar year, the time it takes the Earth to make a revolution around the Sun is 365.242 days. So going back to the lunar cycle and correlating it with the solar year, there’s 29.5 x 12 = 365.25 days.
Thus, the senators deciding that the calendar would be 12 months, with the addition of January and February. December stayed at the end of the calendar. (And every four years February gets an extra day in order to keep the calendar straight.)
Because December is the final month, it is understandable that it is a place from which what had occurred during the previous 11 months is considered.
Like the people who died during the year.
