The main idea behind market and product research is to be able to develop an ongoing awareness of and sensibility to the market(s) and users, not to search for the absolute truth about what product to develop. Absolute truth can only reasonably be approached incrementally - not right 'outta the chute'.
No Market / or not easily reachable.
If there is no market... well... 'nough said.
A market that is not easily reachable, for various product, distribution, funding, segmentation or size reasons (among others), can doom a PD business effort by sapping capital.
What to do about it!
Become knowledgeable about all the parameters that may prohibit the product from reaching the market place and ensure they are properly accommodated. Some common solutions are:
Don't totally reliance on 'neat technology' (there must be a real or nascent market).
Ensure there is adequate funding (a really big problem).
Target the appropriate market segments.
Adequately train Sales & Support staffs and set up proper distribution schemes.