It is hard and only a shock can do it. But telling them to not be afraid when they are has never worked.

As a kid i was afraid of peppers because of the name, but i didn't know green peppers was not hot. No amount of convncing would work even when your might Dad told you so.

So when i was not looking he stuck some in my mouth and i freaked out. And all he kept saying was is it buring is it burning..Finally i realized it was not burning and then i learned.
You can only force things on others when you have complete control over said thing. He knew that pepper was not hot because he grew