In Genesis 15:4 God promised Abram a son. God never said when the child was going to be born. In Genesis 16:1-4, Sarai and Abraham seem to get impatient with God and decided to do things using their own reasoning knowledge, and intellect by allowing Abram to sleep with his maid instead of waiting on God.

When God promises us something, at times we, can get a little impatient and do things our own way. We do something God has not instructed us to do but, want God to bless it.
We invest money into a get rich quick scheme and want God to bless it.
We drop out of school in order to get quick money and want God to bless our finances.
We stop taking medicine and want God to heal us.
God is not obligated to bless something He didn’t authorize.

Listen to the voice and God and rest in His promise. Whatever He said He’s going to do, hold Him to that word.