They are talking about vitamin supplements, not literal vitamins that you need in order to live. Vitamin supplements do not survive in a budget reduction spreadsheet - they're easy to let go of for a while. On the other hand, if you're in pain, you need painkillers, and you're not going to be thinking about your budget, you're just going to go get some to get rid of the pain, even if it's just a temporary fix (and even better for the business if it's just a temporary fix - recurring revenue!).

That's the whole thing, the whole "solve a real problem" thing they keep talking about for startups.