I've worked on a few side projects over the years. Sometimes they've turned out well, and other times I stopped working on them. How do you know when it's time to throw in the towel and when it's time to push through?
Roughly a year ago a friend and I were working on a bill splitting system. It was supposed to solve the problem of splitting bills between friends. More specifically, splitting regularly occuring or one time expenses between roommates. Rather than worrying about having cash, or writing a check and waiting for it to cash, we built a system which piggybacked off of paypal's API to send bill and payment notifications via email, which would generate a web checkout page where the debt could be paid online through paypal.
See how long the previous sentence is? Sounds too complicated already and I'm the one who built it. The eventual idea was that we would wrap this in a native client wrapper, so that if you're out to dinner with your friends you don't have to worry about splitting the bill. One person will pick up the entire bill, split it and send bill notifications via email to all the other people. Then the others pull out their phones and enter their paypal accounts and send payment for their portion of the bill. The bill can be settled on the spot.
Not Every Idea is a Hit
In a perfect world every side-project would be a hit that turns into a business that generates lots of profit for little work. In practice this actually can be quite difficult to pull off. Furthermore sometimes those big hits aren't actually big hits when they start. It make take a couple of years of work to pull. But how do you know if your idea is taking a couple of years to get started or simply not good at all? Nobody wants to be a quitter, and worse nobody wants to quit a good idea that ends up making someone else rich. But there's also more to life than money.
After working on this idea for a few hours a week for a couple months we eventually decided to scrap it. There really didn't seem to be a simple way to make money with this idea. It may have been a useful service, but there are already similar free services out there for this. Over the years, I've grown to have an affinity for ideas that have monetization strategies that are simple to understand. In my experience, the more complicated it is, the less the likelyhood of actually making money.
Most importantly I wasn't particularly passionate about the idea, and I didn't like the idea of piggybacking off of Paypal because of their horrible customer service (I recently had my funds availability delayed for 3 weeks with no explanation, and I've had an account for 7 years and an ebay account with perfect feedback). But using another online payment system made the idea less useful because other peer to peer payment systems simply aren't as ubiquitous.
Benefits of Side Projects
Often the benefits are not monetary in nature. In the case of this bill splitting website, I used it at the time to keep up to date with rails 3 and refresh my skills a little bit. I was using Merb for most projects at work at the time. Furthermore, working on small side projects now and then keeps you familiar with how to start a project from scratch and increases the breadth of your knowledge. If its a small project with just one person working on it, you have to be the one to do everything (or at least hire the contractors that will do the part outside your expertise, which is a skill in itself).
The most important thing is to simplify your idea. Then build the simplest thing that could possibly work. Then keep at it and don't be afraid to re-evaluate your idea. It doesn't make you a quitter to throw out a project that no longer seems reasonable.
Check out an older post of mine about side projects.