Yes-man or yes, God
An employee puts in extra hours to comply with his boss's orders even if it's his rest day. During staff meetings, he agrees with every suggestion raised by colleagues even if he has a different opinion to share. When asked to help out in something, he accommodates them even if he's tired. He feels that to say no is to be selfish and disobedient.
Mary is a model of obedience. But she is no yes-man. In giving her yes to God to be the mother of His Son, she still used her free will. In the Gospel, when Mary was told of her vocation, she responded with a question, “How can this be?”
Her response was not out of doubt (can it be done?) but a matter of how it will be done since she had no sexual relations. Upon learning that it was to be done by the power of the Holy Spirit, she gave her wholehearted yes, even without understanding what her yes would mean. Mary's obedience stems from her great faith, love, and trust in God.
When your heart is attuned to God, there is nothing that God will ask of you that you can say no to. Make your heart like Mary's.