The real factor is whether or not your spouse takes care of the children completely. Or if you have your parents at home taking care of the kids. Because from

The real factor is whether or not your spouse takes care of the children completely. Or if you have your parents at home taking care of the kids. Because from my own experience, taking care of a newborn with the two spouses both working demanding jobs is extremely, extremely hard. It's just about the hardest thing I've ever done, and my wife agrees. We are both exhausted every day, weekends are even harder than the weekdays, and time to ourselves is the most precious commodity we have and the thing we have the least of. If you can't have your parents take care of the kid during the day, or if you can't afford a nanny, then the issues related to day care compound the situation a great deal. If one of the spouses agrees to completely take care of the kid, it makes it a lot easier to spend the extra energy, because it gives you the flexibility required to do things that startups need. The thing that is the most limiting is time and schedule flexibility, and energy. Without that flexibility, the ability to go beyond what is expected is extremely hard, in my own experience.