It’s pivotal that Luke doesn’t have patience. He doesn’t want to finish his training. He’s being succumbed by his emotional feelings for his friends rather than the pratical feelings of “I’ve got to get this job done before I can actually save them. I can’t save them, really.” But he sort of takes the easy route, the arrogant route, the emotional but least practical route, which is to say, “I’m just going to go off and do this without thinking too much.” And the result is that he fails and doesn’t do well for Han Solo or himself.
It’s the motif that needs to be in the picture, but it’s one of those things that just in terms of storytelling was very risky because basically he screws up, and everything turns bad. And it’s because of that decision that Luke made on [Dagobah] to say “I know I’m not ready, but I’m going to go anyway.”
— George Lucas