We go through life doing things we may not even know why we are doing it.
They are usually traditions and customs being passed down. Since birth, you would have celebrated this one very special day, the day which you have come to existence. Many people will make this day special, getting gifts, partying or simply, having a delicious cake.
It is a rite of passage when it comes to those special milestone birthdays. The one thing that is usually the most important one would be the birthday cake. It is typically being beautifully decorated and then lit with candles.
Only the birthday boy/girl gets to make that silent wish. While the number of candles is often the indication of the age, it is commonly being substituted by a number candle. It is usually due to convenience that one would opt for something more practical, in this case, a number candle. What is considered interesting is, despite being separated and divided by physical boundaries, we humans share a lot of commonality.
The celebration of birth is one remains universal.