I think 9-5 is history now. There are rarely jobs which are 9-5. Most of them are 11-9.
When someone thinks of quitting 9-5 job there has to be an alternative which they have to do in life. 9-5 jobs gives a purpose of life for many of them. Without the job life becomes purposeless. And when your mind starts realising this then your organs one by one start giving up. So it has to be well thought.