IMO the only reason why people run into trouble is because they code as if everything completes instantly. For example, they’ll write to disk assuming the operation is quick, because that’s what they’re used to. You see this all the time in all sorts of software when it freezes up and errors cascade.

People just code like everything works all the time. Then when they want to integrate an external service, they have to rewrite everything.

If you understand that network calls have to made and electrical signals have to pass down a bus when you write either a monolith or a microservice, going back and swapping services is super easy.