I was quite excited to read this, having heard quite a lot about it in other books. Unfortunately, although I finished it, I found it unsatisfying and incredibly difficult to read. I'm from a relatively academic background, but it's dense and very hard to decipher.
The basic premise is that what we think of as 'personality' isn't personality - personality is what a more enlightened person has when they transform themselves and move to being a more constructive, socially-minded person in support of society (and this in itself bothers me, because what of harmful societies? Dabrowski seems to gloss over this and assume that all mature societies breed enlightened, only-positive personalities). This personality is only reached through disintegration, the process whereby old (self-serving) instincts are done away with, and the person rises up into a new figure. The process isn't entirely painless, and can be caused by trauma, or result in depression etc.
There are some examples of people who have developed personality (Michaelangelo etc.) and that's basically it.
Tl/dr - training montages are a thing, personalities are only made of positive attributes, developing them is hard and traumatic.
All of this within 238 incredibly dense, virtually unreadable prose.