I've brought up divorce several times in this thread. Or what about getting laid off from an industry with skills not translatable like coal mining? These people may have started out with two incomes or a good paying job, but their circumstances changed. Preparation is nice but often life doesn't care about plans.
I get this type of thing...but I also would state, what did you do to prepare if the job or chosen career disappears. Here's my personal example, I've posted this before.
In 2004, I had a great job, not making big money but more money I had ever made in my life. I was single, and cash positive. Unfortunately, two different jobs, I lost 100% of my retirement that was company stock in nature...both companies went belly up, therefore the retirement they gave us disappeared damn near overnight and we couldn't convert it to something else. I wasn't in big debt, but I had a massive truck payment at the time.
I was apartment living at the time, and wanted to get my own place for the first time in my life. I knew I could get a loan to buy a lot of house...but at that time, it didn't seem right to as a single income, to go into what the banks wanted me to do. I had to completely start over with my retirement in my 40's to catch up with. No bank wanted to loan me $50k. I couldn't get a loan for a cheap place. But $200k, hell yeah sign here, house or condo is yours.
I wound up borrowing money from my mother and buying a mobile home, a cheap one at that.
Why? Because I knew at some point, chances are at some point, the business I was in (telecom) was going to dry up into wireless. Which a decade later is EXACTLY what happened.
What I'm saying is...that decision right there saved my ass the last 3 years cause I've been mostly unemployed, and suffered various ailments to where I couldn't work if I wanted to most the entire time.
I planned for something bad happening. I had savings, I was 100% debt free. I lived frugally those 10 years. I've been able to survive this miserable 3 years because I planned for shit happening way ahead of time.
I may be off the mark, but my bet is not many people do that.