That's often a problem with designers -- they only make a happy flow and only the end of it. No in-between states, don't understand the latency and errors exist

That's often a problem with designers -- they only make a happy flow and only the end of it. No in-between states, don't understand the latency and errors exist, don't dig into boundary conditions and edge cases. It's a typical no-my-job-svg response to boot the problem upwards so their manager will make them aware of those pesky things.