Choosing two or more fonts to use together can be tricky. You want the fonts to complement each other, but not be too similar — different, but so wildly different that they clash. Avoiding these extremes of too little or too much contrast often ends up being a process of experimentation and trial-and-error — like Goldilocks testing out the three bears’ porridge and finding one too cold, one too hot, but one “just right.”
I learned about combining fonts in my Digital Writing and Publishing class this semester. It was my first intorduction into to typography and "font studies". When creating my OPP and the deliverables for my SLP, it was something I had to actively compare because I wanted everything to look cohesive. Your eye doesn't really pick up on appropriate combined fonts, but it DOES pick up on inappropriate combined fonts and it's jarring.