Plan b, a good idea?

Sci Am looks into the question.

...that merely contemplating a backup plan can reduce the effort you put forth to achieve a goal, thus hurting your chances of achieving it. Most people think that making a backup plan is always a good idea, and previous scholarship has focused almost exclusively on the benefits of planning. However, we highlight an unintended cost of making backup plans: a lower chance of successfully achieving your primary goal.

On the other hand:

Image from here, but a dozen versions are out there.

and

Image from here.

Workwise, I don't know how family fits in.
The question was discussed on Quora where the responses were about equally for and against.

Elite Daily is pro-Plan B:

More Options, Less Stuck
The more options you have in life, the less stuck and miserable you will feel.
We feel trapped when we find ourselves stuck in one mode of living, unable to move out of that mode. It makes us feel worthless and miserable. At this point, we will do anything to get out that situation and sometimes even commit to doing dumb things in the process.
If you have a Plan B or even a Plan C on which you can fall back, you won’t feel trapped. In fact, the more options you have, the better you will feel about the outlook of your life. You will likely be positive and optimistic about the future and where your life is taking you.

While Forbes is against:

In the past I had Plan B patiently waiting in the wings while I tried to get what were some truly great ideas off the ground, and guess what? Plan A didn’t work. This time was different. I had no Plan B. I had to succeed. And I did.
Doubt is not your friend.
“Necessity is the mother of invention” even after 500 years. If you really believe you’ve created something that people truly need, then keep pushing forward and quiet that annoying voice that says it won’t work—whether its somebody else’s or even worse, your own. Shut it up and join the mighty minority—the few of us that don’t just come up with great ideas but execute them, and don’t get freaked out when the realities, hurdles and roadblocks of execution set in.
Execute like your life depends on it. Because it does.

I want to write a book - I am writing a book - but I am also looking for work right now.  I don't know if I have the confidence to drop my job hunt to focus on writing.  Maybe I need the kick in the ass of having no plan B.  Maybe my son won't mind going hungry for a few weeks... Yeah, a plan B makes sense to me.