Answer:
The role of driving force.
Step-by-step explanation:
Lying play here the role of driving force for the jack to be Ernest in the future and have a brother in reality. This lying that he is Ernest will change and lead him to be Ernest in the future. If he does not lie about being Ernest, he did not try to become Ernest in the future so we can conclude that this lying is a driving force which compel Jack to be an Ernest in the coming future.