Only because we havent had faith in god and we havent forgotton, making our prayer of none effect.Example: if you forgive someone but havent forgotton the transgression then you never truly forgiven that person you are holding a grudge no matter how serious or great the offence against you.This applies to our selves and towards god aswell,if you ask god to forgive you and you believe he has forgiven you, then dont dwell on it, forget the matter and move on.Same thing when you ask him for something and you believe he will do it. In otherwords have faith in him, believe he will do it, do so but dont doudt or question it afterwards because then you have lost your faith and made your prayer of none effect.You work,you have faith that your paycheck is there at the end of the week.So likewise faith is the substance of things hoped fore.When i pray,the words "I BELIEVE" comes to mind when im through praying,then the wait is on.But remember he gives what we need not what we want.Scincerely I hope this helps God bless.So be it