I really love the timing of Kylo Ren’s outbursts. They don’t come when things go wrong. Most of the time, he maintains a rather calm demeanor. At one point, he even taunts General Hux that a clone army would be better. His outbursts happen when he gives into his own weakness.
BB-8 escapes Jakku. He doesn’t bring out his saber until the messenger reveals that it was Finn who helped the droid. FN-2187. The same stormtrooper who he saw in the village. The stormtrooper who Kylo knew wasn’t behaving the way he was supposed to. The stormtrooper he could’ve had killed or sent away or done a number of things to. But instead, he let his suspicions go and gave FN-2187 another chance under Captain Phasma.
Rey escapes her imprisonment. He knows it’s entirely his fault. Leaving a single stormtrooper to guard over someone strong in the Force? He could’ve knocked her out, done something to her legs so she couldn’t have moved, left droids to torture the information out of her. But he left her as ‘his guest.’ Restrained but unharmed with someone nearby to help/guard/move her in case something went wrong.
He doesn’t lash out because he’s angry at others. He lashes out because he’s angry at himself. Because he failed. Because he was weak. Again. Because, despite his desperation to be like Darth Vader, he is still being swayed by the light within himself. And it’s breaking him apart.