Congrats on your respiration system

Why do people applaud after a person blows out the birthday candles on their cake?

I can understand why we might rejoice in a six-year old child's ability to blow out the half a dozen candles that adorn his or her cake, but shouldn't this tradition end sometime before we enter adulthood?

Think about the customary birthday cake sequence:

We sing happy birthday to the honoree and then clap.

Then he or she blows out the candles and we clap again.

Why is this necessary?

Last weekend I...