Kyp Durron on his power
"When I was still a teenager, I was able to reach into the gravity well of a gas giant and pull a spacecraft out of it. That's something that not many Masters could accomplish. I could do it because I was strong in the Force ... and because I had absolute faith in my right, my need to use that craft for a specific purpose. But I doubt I could do it today. I'm no weaker in the Force, and I'm a lot more skilled... but today I'd know that my intended purpose was not a good one, and this knowledge would deny me the focus I needed then to perform that task. So was I a Master then, or am I a Master now?"
I think this quote clarifies how Kun affected Durron and why Durron failed to live up to Skywalker's initial power expectations.