If you are only in this for the "good parts" then you should just quit now because there are more "non working" times than there are working. The good parts do not come close, time-wise, to the hard working parts.
Here is the key I think, as Seth states below, you have to actually embrase the hard working times. Get in there and get your hands dirty. Stick your neck out. Take a chance not knowing where you will end up. I will admit that most of the time when I do that, I end up in a much more interesting and better place. Stop being so afraid of failing and of what your friends will think, and of what your colleagues will think, and just do it. Or chose something else to do that is safer....wimp.
Just the good parts-Seth Godin
"I want to be an actress, but I don't want to go on auditions."
"I want to play varsity sports, but I need to be sure I'm going to make the team."
"It's important to sell this great new service, but I'm not willing to deal with rejection."
You don't get to just do the good parts. Of course. In fact, you probably wouldn't have chosen this path if it was guaranteed to work every time.
The implication of this might surprise you, though: when the tough parts come along, the rejection and the slog and the unfair bad breaks, it makes sense to welcome them. Instead of cursing or fearing the down moments, understand that they mean you've chosen reality, not some unsustainable fantasy. It means that you're doing worthwhile, difficult work, not merely amusing yourself.
The very thing you're seeking only exists because of the whole. We can't deny the difficult parts, we have no choice but to embrace them.