First of all, you have to really love your startup. Programming all day, then getting home and have to do the same job in the night can be really draining. Sec

First of all, you have to really love your startup. Programming all day, then getting home and have to do the same job in the night can be really draining. Second you have to make it profitable as soon as possible, so you can leave your job and at least start contracting 2-3 days per week, leaving full days to work on your startup. Third, the sacrifice depends on the nature of your startup: if it's a no brainer like a management tool and you're a smart programmer, you won't need to get mad. But if it's really techy, then you better find some mate to not get lost in the venture and use up every minute of your free time. That's my experience and what I've seen around the community here.