“If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you.”  
John 15:7

He says you shall ask what you will and it shall be done unto you; even if such a request has never been made before, it will be done for you, but you have to abide in him; stay where the answers are!
Worrying, complaining and physical observance would not have in anyway caused an 90 year old barren woman named Sarah to have a son, so instead of those options, Abraham gave glory to God and remained in God’s yes! God already told him “yes, he would have a son”, and so he remained in that word.
The Bible says in Christ, all of God’s promises are ‘Yes and Amen (verily, verily, it is so!)’ remain there!
Let the word abide in you, take in his word- hear it, meditate on it, talk it:
“This book of the law shall not depart out of thy mouth; but thou shalt meditate therein day and night, that thou mayest observe to do according to all that is written therein: for then thou shalt make thy way prosperous, and then thou shalt have good success.”  Joshua 1:8
He says YOU would make your way prosperous, and have good success (success that will last!)
“Meditate upon these things; give thyself wholly to them; that thy profiting may appear to all.”  1 Timothy 4:15
He says certainly when you meditate on the word of God, it will profit you and such a profit cannot be hidden. The person that has decided to listen to the word, meditate on the word and remain in the word would always have answers, would always be prosperous, would always have good success!