Kate's take, in a sentence or two

Kate explains that "everything sells everything" means that running any promotion doesn't just sell the specific thing being promoted—it puts her whole audience into "buying mode," and people often end up purchasing other things sitting nearby instead. She points to her birthday sale as proof: the promoted deals only brought in about $11k directly, but total revenue that week hit nearly $26k, showing that attention in one place spills over into purchases everywhere else. Because of this, she tracks total revenue during promotions rather than just deal-specific revenue, since focusing only on the promoted item would massively undercount what the promo actually did for her business.