Jesus' answer leaves the lawyer unsettled. He is caught in his own little legal trap. He asks another question, this time a self-justifying question. We look for loopholes in the Law, exceptions, contingencies and circumstances. We play with the definitions, we stretch the boundary lines, we mess with the commandments.
Legalism plays word games.
We try to make the law practical and doable. Don't give me vague, open-ended commandments. Give me principles and programs. Jesus tells a parable. Be careful around Jesus' parables.