Luke is an ordinary farm kid in outer space. He doesn't like his lot in life, but he is faithful to do his duty. Now let's count the coincidences:
1. When the two 'droids that the Princess sends to Obi-wan land on the planet Tatooine, they get picked up by scavengers and sold to whom? Luke's uncle. (But Luke spends more time with them than the uncle.)
2. The all-important schematics that reveal the weakness of the Death Star are hidden inside the R2D2 'droid and are now in the possession of whom? Luke.
3. Although Tatooine must be a fair-sized planet, Obi-wan happens to live relatively near to whom? Luke
4. Obi-wan knew Luke's father and tried several times to give his father's light saber to Luke (the uncle had forbidden it).
5. Luke now has the Death Star plans, and a guide, and a cool weapon, but wait--that's not all! Despite what he has been told, Luke is the son of a powerful Jedi knight. In fact, by sheer coincidence, the Force is also strong in Luke. Now, if only someone could teach Luke the ways of the Force... Oh, Obi-wan can do that? Wonderful.
See what I mean? Luke is a classic reluctant hero to whom we can relate, but he's also the recipient of a truckload of coincidences. He's an ordinary kid who refuses to blast off to adventure among the stars because of the coming harvest. Then storm troopers kill his aunt and uncle, thus propelling this son of a Jedi into a series of inevitable events that all revolve around him. True to form, humble Luke has little confidence in himself and for a long while doubts he will ever get the hang of using this Force thing. In this way, George Lucas made Luke a larger-than-life individual, but a hero with universal appeal because of his humble beginnings and lack of self-confidence. Even without the Force, we "become" him to save the universe.
Are you an author? If so, you might need to inject a coincidence here or there. But do so with caution until you become a Publishing Master. Too many random coincidences might Force angry readers to hurl your book all the way to a galaxy far, far away.
Now a new question comes to mind: Did George Lucas purposely embed himself in Star Wars by naming the hero "Luke S."?