(My response below, to the above question on Quora)
Failure has many dimensions in the context of a startup and the founder of the startup.
For example: Failure could mean that you have not been able to achieve the numbers (revenues, or customers/users). However, it can still be a fairly profitable business at a lower scale than what you had estimated. If you have raised capital from investors, they may see a venture that does not scale as a failure. The founder may not.
Likewise, failure could mean that while the concept was good, the team was not able to execute well, or they ran out of money because they were not able to raise capital. In this case, the startup SHOULD NOT have failed, but it did not work out because of inexperience or lack of execution capabilities.
So, when people generalise that 8 out of 10 startups fail, it generally means that 8 out of 10 startups are not able to go to the scale or in the direction they assumed it would. It MAY or MAY NOT be a failure for the founders.
Also, it is important to recognize that very few startups fail because their product was bad. They usually flounder because of issues on areas like execution, processes, capital, etc. I have seen many, many founders start off without even talking to potential customers. This is usually a recipe for a disaster as your own views may or may not hold good in the market.
My belief is that while the number of unsuccessful attempts are quite high from among the ones that started off, the percentage of failures comes down significantly among those who had put good thought into their concept and business around the concept BEFORE starting off.
If your question was out of fear of failure, I would urge you to think again. Plan your venture well, understand the market and then take the leap of faith. Check the LinkedIn status of failed entrepreneurs. They either get started again (and investors like to back them) or they get good jobs (corporates like failed entrepreneurs because of the enterprising spirit and the learnings they bring with them). So, while your venture may not succeed, you are unlikely to fail if you pursue the path of entrepreneurship.