I've done both.<p>I started Swell Technology in 1999, ran it for seven years as the only stock holder. I made a pretty good living, worked on interesting problems, drove a 350Z, and had an office overlooking the corner of 6th and Congress in downtown Austin.<p>Now I'm a 47.5% stock holder in Virtualmin, Inc. (YC has 5%, and my co-founder has the other 47.5%). I work out of the second bedroom in a rental house a couple blocks away from downtown Mountain View, CA, make barely enough money to cover the rent, and don't own a car. But, having a co-founder is a still lot better. I fully expect that in a year, the success I had with my previous company will be dwarfed by what we can achieve with the new one, and a huge percentage of that is being able to share the load.<p>I worked all the time with my old company. For seven years running I never took a real vacation. The sound of a ringing phone makes my stomach hurt due to the constant support calls with my old business (so now, I don't have a phone...we have a bug tracker and public forums to help customers).<p>It's entirely possible to start a company solo. But there are some things you'll want to avoid. If you see yourself in any of the following situations, it is time to change your business:<p>1. More business than you can handle solo, but not enough revenue to hire help. You're in a bad business or not charging enough. Change something.<p>2. The mundane (taxes, paperwork, legal compliance, sales or support calls) is taking more than 25% of your time, in order to make ends meet. Pretty much the same reasons as in 1.<p>3. You realize that the "right price" on your products is such that you'll never be big enough to hire employees, even if 50% of the available market buys what you're selling. If you can't expand the available market, then you're in a bad market.<p>With a co-founder a lot of these things are more immediately obvious...it's easy to keep plugging along when only one paycheck has to be cut each month, and you can tighten your belt one more notch. With two or more, the math adds up, and one of you realizes "Hey, we're never going to build a business at this rate. We need to change things."<p>So, sure, there is a possibility that you'll be Markus Frind or Joshua Schacter. If the idea is really good, and you execute well, you can make great things solo. But the odds are against it.