Sometimes we hurt the people around us accidentally. We kick somebody under the table or cut in front of them in the dinner line. We make a comment that is misunderstood or we tease someone who is in no mood for teasing or we don't speak at all because we're lost in thought and someone takes it personally. Just as often, we hurt the people around us intentionally because we disagree over issues as we act out of our own principles and with our own style. What's more, if you rub shoulder to shoulder with people long enough friction inevitably results as your character flaws collide with their character flaws.
Control needs clash.
We develop a history of conflict with someone where we both feel wronged and wounded. It's human nature. Maybe he was tired of James' and John's constant bickering. Maybe he was weary with Thomas' doubts. Maybe his brother Andrew had been getting under his skin, as only a brother can.