This question of "who is my neighbor" in Luke 10:29 can be used by Satan to deceive us in more than one way. Not only can he deceive us into thinking we have fulfilled the command to "love thy neighbor as thyself" when we haven't, but he will also try to apply this command in a way that condemns us who are seeking to fulfill it, by making us think we are not doing enough.

We cannot meet the needs of every single person in the world. Jesus wasn't teaching that. This wounded man was directly in the path of these three men. The priest and the Levite had to walk around him. Jesus is simply teaching that we should take advantage of the opportunities we have. The fact that we can't help everyone is no excuse not to help anyone.

Jesus, through this parable, defined a neighbor as any fellow human being who crosses our path and is in need of our assistance. The Samaritan went to the full extent of his ability and beyond  to help the man. The priest and Levite did nothing.

There was a racial and religious hatred between Jews and Samaritans. Devout Jews would not associate with or even talk to a Samaritan. The priest and the Levite that passed by this wounded man were his fellow-countrymen, and yet they didn't help him. This Samaritan, who was considered by religious Jews to be of another nationality, was the true neighbor. Jesus made it clear that we can not define "neighbor" on the basis of our geography or our familiarity with someone. A neighbor is anyone that God puts in your path.