In the time of Jesus, the road from Jerusalem to Jericho was notorious for its danger and was known as the "Way of Blood" because of the violent robberies that took place there.  Martin Luther King Jr., in his "I've been to the Mountaintop" sermon, described the scene:

"I remember when Mrs. King and I were first in Jerusalem.  We rented a car and drove from Jerusalem down to Jericho.  And as soon as we got on that road I said to my wife, 'I can see why Jesus used this as the setting for his parable.'  It's a winding, meandering road.  It's really conducive for ambushing.

And you know, it's possible that the priest and the Levite looked over that man on the ground and wondered if the robbers were still around.  Or it's possible that they felt that the man on the ground was merely faking, and he was acting like he had been robbed and hurt in order to seize them over there, lure them there for quick and easy seizure.  And so the first question that the priest asked, the first question that the Levite asked was, 'If I stop to help this man, what will happen to me?'"

King continues:

"But then the Good Samaritan came by, and he reversed the question: "If I do not stop to help this man, what will happen to him?"

And with this statement King spoke, and still speaks, directly to the two important questions at the heart of the parable of the Good Samaritan:

"Who is my neighbor?"  And "What should a neighbor do?"