This is a great question and I'm glad it comes up. I'm trying to find a picture that can represent this.
Let's take a leap into Remodeling (and Repair) reality for a moment. Undesireable Stuff Happens-- more-so without planning, research, experience or foresight. But, even with good preparation there are still surprises, unknowns.
Secondly, projects that last a while will likely wear on the good nature of the occupant, and maybe on the contractor too. Having someone from outside the family becomes imposing and aggravating due to privacy. It also imposes because of noise, dust, debris, interruptions of normal patterns, delays, undpendability of people. There can be disagreements about the work, the color, the imperfections, the style or design, the time, the cost, etc.. And all this assumes that the contractor is Business, Management, Technically Competent, Honorable, Responsible, & a Communicator.
Is it becoming apparant how the contractor-owner relationship might affect someone's ability to "live with" what's going on in their home? And do you see how it can affect your ability to keep some control, and help avoid a catastrophe? And perhaps how without that foundation a project is doomed. Doomed to stress, illness, harmful work that needs correction, higher costs, consequences of stress in other relationships, at work, etc..
So, even with a good match, a solid open relationship with good communications contractor-to-homeowners, there will still be problems that need solving. It is only rational that with such a relationship comes a much higher probability for success... and a long term friendship (so there can be a next time).