fonts - How to know which second typeface should be used, given a contextual typeface?

When searching for how to "italicize" a word in an italic context, I come up with an idea that changing the typeface is the solution that still convey the psychological effect that an italic-in-roman word normally does.

For example:

But how do I know which typeface should be used, given a contextual typeface? My choice of Arial in the example is merely because I feel it's right, not really based on any explanation. What knowledge of typography that I'm missing that can explain this phenomenon?