When I was younger I asked my father who his best friend was. He replied without hesitation, your mother. I repeated the question because I didn't think he understood, he answered the same again. I explained to him that I meant out of his friends Phil, Brian, Mark, and Todd which of them did he consider his best friend? He interrupted before I could finish,
"Son, she is my best friend, I do everything with her and don't want to do anything with anyone else." I understand what he means now.