Finances
The first and most obvious. People work in order to bring home the bacon, so unless you're in sales and used to working on commission, cutting off your main source of income for a job that doesn't have an income isn't usually the most promising way to pay the bills. You might strike it rich, but what if you don't?
Time
It's an illusion to think that starting your own business is fun-and-games, not a "real job", or "more flexible" than working the corporate 9-5 job. What tends to happens is that work and personal life bleed together, and more often than not, work takes over, eating up all your time.
Career
If you're in a great job with benefits, meaningful projects, and an amazing team, and leave to work at a startup that bombs, can you get your old job back? Companies move on, and taking the entrepreneurial route may not land you back at the same place you started.
Family/Relationships
Going back to the "time" risk, if entrepreneurs aren't careful to balance their priorities, the business can and will take time away from other important aspects of life. If this isn't kept in check, relationships can suffer, especially with the stress that comes from the late hours, financial famine, and other factors of working in a startup.
Opportunity Cost
What could you be doing with your time and money instead of starting a business? Working at that "great job"? Going back to to school for another degree? Traveling? Saving or investing money? By choosing to start a business, you're generally choosing not to do these other things.
Stress
Being an entrepreneur is a marathon in problem-solving and crisis management. There is almost never a time, especially at the beginning, when things are not breaking down, running out of money, being held up, or not progressing quickly enough. Can you hack it?
Failure
Suppose you spend all your time, money, energy-- and everyone else's time, money, and energy around you... and the business flops. You don't get rich, in fact, you get sacked with debt that makes your old college loans feel like chump change. Failure, failure, failure. It's definitely a possibility-- how many startups are still operating after the first year? Five years?
For a blog encouraging entrepreneurship, that was a little heavy! But my point is this-- these risks (and more) are a fact of life for entrepreneurs. Here's another article about entrepreneurship and risk-- I love its tagline, " A hammock out back is comfortable. La-Z-Boys are comfortable. Entrepreneurship? Not so comfortable."
So, which is the biggest risk? I think it's the one that you're not aware of and already making a back-up plan for. Since it's not something you're actively thinking about in your business, it could be more likely to happen. And that’s the real risk you don’t want to take.
