Why we fall in love

did any one ask him self why did i fall in love?

do we fall in love because of the attitude of the other person , the apperance , the way of talking , or maybe because we need some one to  be a witness of our life for our existence ,some one to share us the good time we have and be there in the bad one , but how do we know that this person is the perfect match , how can we be sure that you will not get hurt if you say the word ( I love you )