Founders generally fall in the category of knowing enough to see an opportunity, but not enough to see the obstacles. Which is normal, as otherwise they wouldn’t start in the first place, but this means that they need to rely on a community of people to get feedback, guidance and to learn from others experiences.
I’ve had a couple of instances of late where entrepreneurs with very viable businesses are told that their idea is not feasible, not scaleable or not worth their while. It normally comes from a VC (or incubator). The advice is not wrong – possibly misplaced – but the one thing you need to be very aware of is the motivations and perspectives of the person giving you advice.