I just spent three weeks at a Zen center and am reminded of what I already knew from experience: There is no substitute for structured training with a competent teacher.
Since I have written about the dark night more lately, I can add that I suspect that the processes inherent in a dark night (switches into the opposite end of polarities, disowned voices surfacing, disidentifying with familiar identities and viewpoints) happens in such a setting as well, but often in a more stable and slightly easier way. The setting provide support and stability through the schedule, community and teacher, and the sitting provide space for it all to unfold and pass through. Without such a structure, it can go a bit haywire – loss of health, friends, ability to function etc. – as I know from own experience. Of course, there are unique and valuable lessons available within and outside of a traditional structure.