I just saw this thread and wanted to share my experience. I have been trading for almost 10 years while working a day job but haven't been successful until I decided to create a trading strategy that specifically addresses the issue of sustainability in my absence. In other words the strategy must work while you are working, sleeping, and not at the computer watching the market. I first started formulating this strategy almost 5 years ago and have refined it until last year when I finally became consistent at it. However, it has taken me literally thousands of hours of research and testing in both demo and live markets. It isn't easy but it is doable. You can also create a successful strategy to do the same but be prepared to spend a significant amount of time defining it and refining it.
Basically the strategy you decide to build must address the issues of what to do when the market moves (for and against you). Your strategy must address how you enter trades and how you get out when you reach your profit target or stop loss. It must take into account when the market abruptly or temporarily moves against you. You must also address what is the risk you are willing to accept. You must never assume that the market will go the direction you expect. More often than not, the market will not do what you expect it to do. Observe and respond to what you see, not what you hope will happen.
My strategy is a moving average crossover strategy using multiple timeframes and entry/exit points. I trade the forex spot market and currently make more than my day job. But it has come at a price of working nights and weekends analyzing my performance, my personal behavior, and most of all the market. The keys to success will be perseverance, hard work, and being honest with yourself. No one can hand you the Holy Grail; you will have to work for it.