Sit on your own and you can achieve all kinds of mental states, some of which feel really good. Sitting with other people also can feel really good. But hang out long enough with anyone and your karma will appear, boom. There you are, really annoyed at someone. There someone is, really annoyed at you. You know where this usually leads, and it isn’t any place you want to be.
But in a Zen center, when this happens the context is a practice of liberation, not just of ourselves but of all beings. Instead of getting solidified, our karma can start to dissolve. Most of the time we live in a hall of mirrors. Escape isn’t easy. It’s by practicing in community that we can break free.