“Then Sarai, Abram’s wife, took Hagar her maid, the Egyptian, and gave her to her husband Abram to be his wife, after Abram had dwelt ten years in the land of Canaan.” Gensis 16:3

This story is an example of a man and wife who took matters in their own hands and disavowed the Word of God spoken to them years ago.
God told Abraham that he would have a son born to Him through Sarah, his wife. They were both old and became tired and impatient of waiting so they short circuited God. They found a temporary solution to meet their needs. In effect, they fell into unbelief.
Ishmael was born but he was not the promise from God. When God makes a promise, He keeps it. Sometimes it takes many years for the promise to come to fruition. Moses tended sheep for 40 years before He was called by God to do a mighty work.
The question is not the efficacy of God but how long you will walk by faith trusting God for something when there is no sign of proof or evidence. Abraham and Sarah gave in to the temptation of sin to meet their need for a child.
The problem when you short circuit God is this action will probably lead to suffering and misery. You are upsetting God’s apple cart and taking a short cut.
You will miss out on the fullness of God for something that is very short lived. God’s promises are eternal and will provide an abundance and richness unavailable through worldly actions.
Wait on the Lord and He will strengthen and encourage you! This is the path that will lead to the blessings of God.
Without faith it is impossible to please God!