There is a BIG difference between doing something part time because you love doing it, and doing it all day every day (including weekends) because you HAVE to. The excitement of 'being your own boss' is quickly ripped away when you realise that you have a thousand bosses - EVERY SINGLE customer of yours is essentially your boss for a short time.
Not that it isn't rewarding, but as others have pointed out in here, you have to go into it with the right expectations. I highly recommend that anyone looking to start a business reads Michael Gerber's "The E-Myth Revisited". It will outline a different way of looking at your business at the outset.
Back to the coffee shop though - unfortunately, a lot of lay people still see the romantic notions around owning a coffee shop, and they all assume that business owners are raking cash in and are out to rip off the poor workers. Here in Australia there was a big backlash recently when conditions around weekend overtime rates were changed, affecting a lot of people in the hospitality industry. Coffee shop, cafe and restaurant owners were castigated by the media and the public for not deigning to pay staff time and a half or double time on weekends etc.
Nothing against paying workers fairly, but I know many friends who run such establishments. For many of them, opening on a Sunday or a Public Holiday is mandated by the mall or premises they are in (written into their lease), and for most of them, weekend trade actually COSTS them money, rather than makes them anything. Unless of course they reduce staff and work weekends themselves, but staff calling in sick or not turning up for shifts mid week usually means they work 7 days a week.
Nearly every cafe in my town closes at around 2 or 3 pm, after the lunch rush because demand is so low after that that it is economic suicide to try and keep the doors open and pay wages etc. for a handful of customers. Bad luck that I tend to try and arrange meetings and do work outside my home office in the late afternoon...