Why more than 85% of projects/products/startups fail?

A fundamental question and its answer requires research in:

What did we want to make/produce?
Is it needed in the market?
Did we involve professionals during the construction process?
Does the team have the right mindset (not the skills)?
Have you adapted to market changes?
Are we initiators or followers?
Did we involve professionals during the construction process?
Was the product launched at the right time?
Have we chosen the best Business Model that is able to keep pace with developments?
Did we involve professionals during the construction process?
Did we arrange the parts of the project according to value priority?

How many times has the question been asked: Did we involve professionals during the construction process?