In other words, sometimes, it's not your choice to be a solo co-founder. Many people have compared finding a co-founder to finding a spouse. In both life decisions, I don't think anyone seriously advocates for "sucking it up, and going with the least bad option."
Sometimes, you're poorly geographically positioned, or in a "strange" market, or later in life (friends are already "matched up" or in secure jobs), etc
For myriad reasons, you could sincerely try to recruit a co-founder and come up short.
The question then becomes ... do you make the best of it and go for it anyway?
Or, is the lack of a co-founder a signal (to yourself and others) that your idea / plan is unworthy?
I hope the answer is the former because that is what I am doing. Someone remind me to write this article when I figure it out.