Ken is a very proud jedi and he prides himself in teaching the younger kids about peace and tranquility within the force and how to reach it. So seeing not one but two jedi Master Zhar personally asked him, a consular, to fence against when he also told him he didn't believe he was the right guy for the job just compacted the issues in the matter for Ken. He wouldn't admit it to himself or anyone but a part of him believes Zhar was slighting Ken in making him do that.