One of the challenging questions for someone who is about to start a business is "should I take the plunge?". The deeper concerns underlying the question are "what if it fails? will I get another job? how will I support my family during the initial years? I am in a comfortable job with a clear future ... why risk it all? ".
This post is my opinion on the matter based on the experience of having started and succeeded.
What if it fails is a question you HAVE to ask yourself. Having a Plan B is critical. At the same time, the imagined risks are almost always higher than the real risks. Even if you fail you are not unemployable. You have a good education, good work experience and you have the experience of having tried to pursue a dream. The Plan B could just be "I will go back to where I was working earlier". Almost every boss in the world, if you leave on a good note, says "would be glad to have you back" and actually means it. So that is backup plan 1. So keep in touch with your boss after you have left so that backup plan 1 is active. Backup plan 2 is to have some money in the bank to tide over the time spent looking for a job. Even bad economic recessions do not last for ever.
Moreover, everyone dreads leaving a job and starting off on their own. It is "sweat your palms, watery belly" kind of dread. The last day of my job at the software company I was working at was frightening for me. I left just after 9/11 happened and most people thought I was being foolish. In fact when I called my father and told him that I had resigned my job he said "You are stupid. If there is a chance, take back your resignation". December 2001 was the beginning of a tough slowdown so everyone I knew, including me, was wondering if it was a smart decision. So if you dread leaving your job, you are not alone. Some of that dread is certainly unreasonable but then when is fear linked to reason.
How do I support my family is too personal a question to lend advice on. But in general I would say "either start off before you get married or marry a person who works or marry a person of steel".
I am in a nice cushy job is the hard one and difficult to answer. If you are a well-educated professional working in a good company, the dilemma you face is real. For instance, you are a Senior Manager at a large consulting company and throwing it all away to start something may not be worth it. The financial rewards may not make sense. Maybe you can become a Partner in the consulting company which better fulfills your goals. In some ways the educated professional has a tough choice to make because he/she has to choose between a well-paying job and an uncertain pay-off. The answer to this question is something deeper.
The core issue that you have to deal with if you are wondering whether to start off is 'know yourself'. This is the most difficult part. Have you sat for an hour just with yourself ... no TV, no drink, no book, no facebook, no spouse, no children and wondered what makes you happy, what you really want to do in life. Personally, I always imagined that starting up something meant you imagined a blockbuster product or service, you made an excel sheet with business plans on it, you reviewed everyone on progress and you watched the company grow. I imagined a world where I was translating an idea to reality. There was also a deep urge to create something that did not exist. The sheer thrill of taking an idea to a 100 crore business that people talk about/are willing to work with you for /that people recognize/are willing to pay large sums of money to buy was my kick.
You should find what your kick is before you start.