There's a huge difference between 100K in Tennessee vs 100k in NYC or SF.
Let's take NYC. The fact is that in New York City, the median household income is about $50k/year. (Last year it was $50,895.) So if we define a "middle class lifestyle" as that which those in the middle can afford, well, by definition you're going to get by very well following that lifestyle while making $100k/year! Even if your household has 3 people in it.
But if you define "middle class lifestyle" according to the way you think that you peer group is living, well, I've known people making $200k+ who experience "trouble getting by".
Now I can understand making more, choosing to live better, and running into financial trouble because of it. But if you do that and blame anyone but yourself, well, I've got nothing in the way of sympathy for you.
I've seen many people complain about not making enough to live where they live, when I clearly see lifestyle changes that would fix the income problem, and I see people living alongside the first who make less and save more.
I don't know you. Or your life circumstances. It might not be true for you. But "$100k/year isn't enough to survive" is the kind of claim that I've learned to be automatically suspicious of.