I think the most common thing that gets drilled into our heads in DPA is subsurface scattering. It’s something everyone knows about – probably because they aimed a flashlight directly against their hands growing up, but no one really realizes how a lot of the materials we see have it.
Fruits being the primary example. It’s so subtle, and in my case, with the banana I’m about to eat, it’s what makes the difference between a render looking really fake or really real. And you can’t really use the same configuration for SSS on all materials since how far a light will penetrate a material varies significantly. Also, it really requires some strategic back lighting.