The question is actually mis-phrased. When people ask the question "Have you validated...", they are not asking for an absolute answer that guarantees success. They are probing whether you have actually thought deeply about what you are doing, how it will work, how it fits within the market, etc. If you haven't done that and can clearly articulate the answers, then the chances of success are orders of magnitude smaller than they otherwise would be.
The chances of success are still very small. 95%+ of startups fail. But, if you haven't done your homework, then chances of success are virtually nil.