To me, Obi-Wan's character arc is fully explained in the OT. "You are reckless." "So was I, if you remember." Obi-Wan starts out as a kind of hot-headed jedi who lets his feelings get the better of him, similar to Luke running away from his training after getting the vision of Han and Leia. He jumps into training Anakin without much thought because he is emotionally attached to Anakin and wants him to succeed, without thinking of the consequences. Over the course of the story Obi-Wan shifts from the hot-headed young Jedi to the wise man we meet in ANH. How exactly that happens. Well I haven't completely worked that out yet.