Answer by Garrick Saito:
The candle is symbolic in nature, carried on through the centuries as tradition.
There doesn't appear to be a single clear-cut origin. There are two schools of thought.
One school believes it dates back to Ancient Greece, where a single candle was used to symbolize the "glow of the moon."
The other believes it was part of a 17th century German tradition to celebrate Kinderfest (which translates from the German into "children's festival"), where the single candle represented the "light of life." The German superstition subscribed to the belief that if you make a silent wish and blow out all the candles, your wish will come true.
In my experience as a kid, they don't really come true, but it's fun to imagine that they might…