Why do people dye their hair?

There are so many célébrités and regular people out there who dyed their hair. I like my natural hair color a lot. No need to change it into anything else. I just wanna know why, that's all. I know that célébrités sometimes dye their hair to get a new part ou to avoid being identified with their characters. There's not that many male natural blonde célébrités out there who remained blondes, yet at the same time there's plenty of dark haired female célébrités who dyed their hair blonde. So, brunette girls want to become blondes, but blonde guys want to become brunettes. That's a very strange phenomenon, at least to me. But why do people, even the regular people, dye their hair in the first place, that's a total mystery to me. Anyone?