Why do recipes that call for vanilla always tell you to add it last?

I've always wondered why this is. Does something happen to the vanilla if you mix it in too early?Why do recipes that call for vanilla always tell you to add it last?
vanilla is meant for flavor and is volatile. If you add it in at the beginning then you will lose some of the aroma/flavor.Why do recipes that call for vanilla always tell you to add it last?
Heat will evaporate it, so it's best to add it to the food once it is taken off the heat. The flavor is more potent that way.
yes..excess heat destroys the delicate vanilla flavor...
vanilla is acohol based and it will evaporate really fast