As we mentioned above, fonts pair well together when there is a certain amount of contrast between them. Here, font weight (i.e. thickness or thinness of letters) is the point of contrast; stout, chunky fonts can often work well with taller, skinnier ones.
This is because it’s easy for onlookers to distinguish between the two fonts, and understand that each plays a different role in the document or project. Both carry their weight (see what we did there?) while serving different purposes – creating a complementary design overall.