How did Advent calendars become a beloved holiday tradition?

(NEXSTAR) - While the chocolates are usually not the finest, it's hard to beat the childhood excitement of opening up the next Advent calendar date to see what small treat awaits.
Advent calendars come in many forms, even catering to adults with small bottles of wine or whiskey instead of chocolate, but how did the tradition begin?
Historic and current German Mercedes cars are wrapped as presents in a giant advent calendar in showrooms at a Mercedes branch in Munich, southern Germany, on Dec. 10