I think a lot of it is context. For example when I lived in Russia, I didn't know kids could be nice to each other. It was a doggy-dog world where I grew up. When I came to Canada, it took me 4-5 years to stop mad-dogging people and relax.
Had I stayed there, being on alert your whole life and dropping dead at 55 would've been very normal indeed.
This is why people who get someplace and then lose it, are the ones who tend to kill themselves, or folks who have a hard time fitting in from the get-go. For most people, they don't know things could be different, so they're fine with what is.
You misheard that phrase or learned it from someone who did. The correct version would be, "It was a dog-eat-dog world." The idiom makes a lot more sense in its correct form as it describes an environment of brutal competition.
I'm glad you find Canada to be a kinder place. I like it here too.
Yes. Personal mental state is a poor indicator of how well things are actually going, because people seem to mentally get used to whatever it was they grew up with.
It goes another way: having some awareness of the situation is actively harmful for the same reason, because it makes it less acceptable mentally.
It might feel that way, but it's really not true. Plenty of people work jobs they'd rather not do, but for most there's at least something they like in it. Even menial labour can be satisfying when the impact of the work is immediate and obvious. When people really hate working somewhere, there's often some specific piece making them miserable, like the hours, their boss or their commute.
Life is a mixture of good and bad, and it's easy to fixate on the bad, but don't forget about the good. It matters too.
This is one of the reasons why I often ask myself why the suicide rate is so low in society.