Okay, pressed for time but I'll try to get something going here -
You'll never work harder (or longer hours, for that matter) than you will for yourself. It's a pleasure that, for those that have intense drive, is a great thing, but some people do grossly underestimate what it takes to make a business work. Of course, this depends greatly on what you want to get into, as if you want to be a professional photographer, that's nothing like what it will be if you want to open a store, and vice-versa. Each industry/field is going to have good and bad you'll need to deal with, and many times you don't know all the "fun" things you'll encounter until you're already knee-deep into your new career.
My wife (then girlfriend) started our business before I met her, but things didn't take off well until we both teamed up and had two heads going into this whole thing we do. It was a very different time for online retail back then, and truthfully, I don't know if we could pull it off the same way now that we did a decade ago. Prior to the giant retailers "discovering" that they could make money on vegan stuff (Zappos destroyed the footwear market for a lot of small businesses that used to thrive on that product base, Amazon has put a pinch on food sales for small shops for those who don't mind stocking up on some things, etc.), it was a very different time then for anything you want to sell online. That's precisely why there were about twice as many online vegan shops like ours circa 2005, times were much better then, you could do plenty to get the word out without spending a lot (we didn't have Facebook/Twitter then, but the other options seemed to work even better at the time than those do for us now). Not to mention, ANYTHING that you do that relies on technology is something that will be tricky - unless you want to live and breathe learning tech stuff along with everything else you do, it means that you'll either need to have a lot more capital to start with to hire others, or, expect that doing it DIY means you may take much, much longer to move your way up in whatever game you get into. I had to cut and run from the bulk of tech stuff years ago as it became impossible to stay on top of what's new while building a business that needed full-time attention. Now I contract more out, but it sure hits the checkbook with a lot more punch to go that route. But, that's enough about online retail, back to general stuff!
You'll be FAR more rewarded by working for yourself when you know that EVERYTHING that happens which is good is a direct result of your hard work. HOWEVER....everything BAD that comes your way is also a direct result of what you do, and when you run your own show, there's nobody to pass the buck to if something goes wrong. Some people have a really, really tough time with that, they love the feelings of success and accolades, but it's having the fortitude to keep pushing when everyone is telling you that your business isn't working, or during those times when you don't know how you'll afford to eat lunch that day, THAT'S what sets a good businessperson apart from someone who can't handle the rough patches. And believe me, you'll have more rough patches than you'll ever know...
I wouldn't trade what I do for anything, but at the same time, I know that I've probably shaved a few years off my life from stress and constant worry about everything. Even when times are good, you know that they can turn quickly, so one BIG piece of advice is ALWAYS PLAN FOR THE WORST. People who take out massive loans and never have a contingency plan for things being less-than-stellar end up in terrible places, so the more you can do without having to borrow from others, the better off you'll be. It may take longer to get where you want to go, but unless you've got someone who can bail you out, taking on big debt to get things moving can be the end-all that shuts you down. Not to mention, unless you have a big savings to live off of, you'll probably want to plan to have a part-time job for at least a year or two just to have enough survival money in case the business doesn't move forward quickly. Either Courtney or myself (and at one point, both of us) had to work full-time jobs elsewhere during our first 3 years working this together, it simply could not sustain itself until we built enough of a base to earn enough to get by. We didn't draw a dime of salary for years, every cent we made was re-invested in our company because we KNEW that if we spent it on ourselves, we'd never get far and had to sacrifice a lot back then. Those were interesting times, to say the least, and ones I'd prefer to not go through again. Everyone I knew looked at me like I was crazy for keeping on trying, none of them said they'd have suffered through all the stress and "will we make our cheap rent this month" days, but it did pay off. However, for every story where one business does work, there are twenty more where people didn't get past the first year or two.
I could rant and rave about this sort of thing for hours, but I do have to pack for a flight in the morning!
"A 'hardgainer' is merely someone who hasn't bothered to try enough different training methods to learn what is actually right for their own damned body." - anonymous