Have you dealt with arrogance?
How did you deal with an arrogant developer?
Step 2. In the scenario that even this does not work or cannot be applied easily, then ask that "If we wanted to test out which option between these two, three approaches will work better, than what test could we conduct ?" Focus on defining a test to validate assumptions, rather than arguing for or against an option.
That might come accross wrongly, ask yourself how you would respond if someone told you the same things you are telling them. Trust takes time to build.
But in reality, I wasn't allowing the junior dev to grow at his own pace, to explore and understand and evolve his way of doing things. I was just cramming process and procedure down his throat...which was not only arrogant, but an extremely ineffective teaching tool.
So in the end, it was I who needed the lesson in humility...not the junior dev. Funny what a perspective change can do.