From ancient times, groups got it that the way to punish miscreants was to isolate them. In many cases they were driven from the community. Out there alone they couldn't make it. No surprise, the Bible, which was supposed to be a civilizing force, warned against the evils of isolation.
Now, the state of California is accepting that isolation is a horror, not an effective tool for either punishment or rehabilitation. The settlement in the Pelican Bay State Prison lawsuit will reform the standard practice of placing supposed prison trouble-makers in solitary confinement indefinitely.
At the very least, sustained isolation drives human beings nuts. Man is a social animal. That was proved with the research on mirror neurons. We influence each other cell by cell. When there are no cells, no pun intended, to interact with, we turn inward - and go mad. Shakespearean tragic characters like Hamlet and Lear took refuge in their own minds.
At the worst, it precipitates suicide. The troubled mind enters an alternate reality. There offing oneself seems like a good solution.
Since CA trends tend to be influential, other states will probably also be forced to review their policies on solitary confinement.