Uhhhhmmmmmm - how to answer that? It's like shedding a layer of skin.
We grow up with expectations put on us (some from society, some from friends, most from parents)...then suddenly the time comes when you have a big 'FU(K IT!' moment.
Realisation hits that all the fear based decisions you've been making all your life (money, career etc) are for $hit (usually someone elses $hit) and climbing the status ladder is meaningless - and then you die.
Usually there's a catalyst for this (job crisis, divorce etc etc) and the bigger the meltdown, the more profound the changes afterwards and the more fearless you become.
It's an important rite of passage - life is too short for faffing.
That's my take on it anyway.