Off the top of my head, not understanding the implications of the 2 Generals Problem is a really big one. Specifically, time and again, I've seen engineers struggle with distributed sagas (or any kind of distributed coordination really), because they don't know enough about the underlying model to reason about it.
There are also simpler issues. Not knowing the difference between GET and POST, not understanding what a header is, how parameters are passed etc...
Then there are the problems in the middle like not knowing how to correctly configure an HTTP client library.
The purpose of writing the book though is to help people develop a good mental model of the system, so that they don't need to memorize a list of all the things that can go wrong.
Adding a few examples to the intro wouldn't be a bad idea though!
There are also simpler issues. Not knowing the difference between GET and POST, not understanding what a header is, how parameters are passed etc...
Then there are the problems in the middle like not knowing how to correctly configure an HTTP client library.
The purpose of writing the book though is to help people develop a good mental model of the system, so that they don't need to memorize a list of all the things that can go wrong.
Adding a few examples to the intro wouldn't be a bad idea though!