Remember "girl math," the viral thought project that had every girl explaining their budget? For example, if you go to Starbucks to buy yourself a little treat and you get yourself a $7 chai, but you used your giftcard, that was free. Or if you buy a skirt, but you didn't like it, so you return it and get cash back, you just made money and can now go buy yourself a treat (like Starbucks).
It sounds silly when you explain it like that, so the girlies dubbed it "girl math." But finance professionals are saying that it's actually just econ. One girl recently went viral with her "breaking news" about how her finance boyfriend explained that the "girl math" she was telling him about was actually a "sunk cost," a common term in the finance world. I'd love to go further into this explanation, but as you can see by my writing occupation, I am most definitely not a finance person and have no idea how to explain it… I'll let the viral video and its commenters explain in "girl math" terms instead!