What makes your best friend your best friend?

What makes my best friend my best friend is that she is nothing like me at all. I like to be crazy and goofy while she's the serious and practical one. We're best friends because our differences compliment the others. My goofiness gets her to loosen up and have more fun while her serious and practical ways have made me learn to be mature at the right time. If my best friend and I were too much alike we would always be getting in trouble and our parents would think that we are bad influences on each other. We have been best friends for 8 years now. We will be best friends for years to come as well.