Ryan McAvoy said:

imperialscum said:

And losing patience in a sense of swiftly ending the fight has nothing to do with anger. He came to the point where Luke was physically cornered and he had move to the final step of his plan.

Screaming in pain when Luke manages to chop a chunk out of his shoulder, was all part of his master plan? Because to me that's the reason he loses his cool and maims Luke 1 second later.

No, getting hit in his shoulder is irrelevant. The plan was to corner Luke and disarm him in order to persuade him to join him. He came to this point when the they moved to the very edge of that small platform. Regardless of Luke hitting his shoulder, there was no space and no reason to prolong the fight.