While telling someone to ignore naysayers and those that say you should go back and work for someone else is all nice and touchy-feely, it is also often dead wrong.
Telling someone that they are just not cut out to be an entrepreneur could be honestly good advice.
My ex-wife was a professional ballerina. She used to get people asking for advice about dancing ballet professionally. She could often simply look at the person and tell that they were not cut out for professional ballet. They may have loved ballet, been passionate and dedicated to ballet, but there was just no way that they were going to make it because they just did not have what it takes to be a professional ballet dancer.
Similarly, there are people that are just not cut out to be an entrepreneur. Heck, I may even be one of them. Telling them to just "go for it" or "follow your dream" is REALLY taking the easy road.
In order to give really good advice about this you need to get to know the person. You need to know what their goals are and how the business they are talking about fits into (and drives) their life. This is much harder than reviewing a business or marketing plan. It is much more difficult than assessing a market or opportunity. It requires real honest knowledge of the person and their life goals. It requires a deep understanding of their likes and dislikes, strengths and weaknesses, their vision and their blind spots.
No entrepreneur is perfect and no business model is slated for certain success. Our job is to provide assistance, insights, and even a push in the right direction.
Sometimes the right direction is away from being an entrepreneur.