What's the value of a PhD?
For some, the value is clear. You want to do pharmaceutical research? Get a PhD and it'll open up the possibility of a well-paid career.
For others, the value of a PhD comes from the way it's perceived by others. It's perhaps less quantifiable, but in some circles the status of having a PhD can be more valuable than the skills you developed on the way.
And there are those who just love their subject and can't imagine doing anything else.
But then there are some for whom doing a PhD carries no obvious economic, social, personal or practical benefit. It's expensive, time-consuming and stressful, so why do it if there's no tangible gain?
The value of a PhD, here, is whatever you believe it is. It comes from the story you tell yourself about what it means. This is as good a reason as any to do it (and certainly more interesting than a cost-benefit analysis). Remember, it's about your story, not anyone else's; other people might not understand, but that's OK.
See also:
Sometimes we can get stuck in these stories. "I need to prove myself". "If I quit I'm a failure". Stories such as these are more likely to add to your distress than to help motivate you. See the blog post below for more on this!