More Star Wars Frustration

What was said:

BEN: When I first knew him, your father was already a great pilot. But I was amazed how strongly the Force was with him. I took it upon myself to train him as a Jedi. I thought that I could instruct him just as well as Yoda. I was wrong.

What's wrong with this?:

BEN: When I first met your father, he was still a young man, but my mentor recognized the force was strong within him. He took it upon himself to train your father as a Jedi, but he was killed before the training could begin. I trained your father and we were very good friends, until he turned to evil.

Why did Lucas make Ben into a liar? Why would Ben lie to Luke? Why would a man make a movie that makes no sense in the context of his earlier film?

I hate you "prequels!" I hate you George Lucas!