Three is a great number. It is heavily utilized in magickal practices as a sort of shortcut to infinity.

Three is the number of creation itself. Think 1=Father, 2=Mother, 3=Creation. Three is the moment itself; three is the magick, the spark of life. The reason it's used in magick so much (lots and lots of shit in magick is done or said three times) is because it IS THAT if you hit three, you've effectively hit all you need. You hit the core. Three is also a number of completion, largely because of geometry (1=point, 2=line, 3=triangle).

Three people are supposed to really have it good. They are, according to the books, "brilliant, gay--in the happy sense, dammit!--artistic, and lucky". Beats the hell out of four.