Vitamins! You don't need to eat if you take vitamins! They can give you energy and fix everything you're doing wrong in your life! Just listen to the salesman!
Unless you either A) live in a third-world wasteland or B) eat nothing but Doritos for every meal, you probably don't need to take vitamins. As a rule of thumb, if you ate some kind of plant today, and some kind of animal, you're probably not doing too bad, nutritionally speaking. But, people without real problems love to invent tiny little problems they can pretend to solve by buying something, and thereby make their generalized anxiety go away a little bit. This has been true ever since humans stopped spending all their time hiding from lions and searching for a bush with a few berries left on it.
Do you have any reason to believe you are malnourished, or are you spending money on supplements because “you never know”? You never know when a giraffe may dent your car. You’d better take out a special giraffe policy. Is it smarter to spend money solving problems you know you have, or ones you can't be sure you don't have?
Mom always made us take vitamins. It made her feel like she was covering all the nutritional bases with her kids. As a grownup, I almost never take them. Then, I found a bottle of multivitamins in the cabinet from last winter, and spent a few months eating one every morning, just because I hate waste. I felt exactly the same as when I didn't take them. But then again, I'm lucky enough to live in a developed civilization where only the truly determined person can avoid getting enough vitamins. This is a data point of one. Purely anecdotal. Do not change your life just because of this story.
Things that call themselves "dietary supplements" may not even have actual vitamins in them. In fact, they probably don't even contain what the label says they do. The dietary supplement industry isn't regulated at all, and they don't have to do what they claim to do. They're accountable to no one. It's a wild west kind of situation. They tend to appeal to humans' deep love of logical fallacies, usually these two:
Appeal to ignorance: Argument from ignorance (in which ignorance represents "a lack of contrary evidence"), is a fallacy in informal logic. It asserts that a proposition is true because it has not yet been proven false (or vice versa). This represents a type of false dichotomy in that it excludes a third option, which is that: there may have been an insufficient investigation, and therefore there is insufficient information to prove the proposition be either true or false. Nor does it allow the admission that the choices may in fact not be two (true or false), but may be as many as four,
3. unknown between true or false
In debates, appeals to ignorance are sometimes used in an attempt to shift the burden of proof.
Appeal to antiquity: An appeal to antiquity is the opposite of an appeal to novelty. Appeals to antiquity assume that older ideas are better, that the fact that an idea has been around for a while implies that it is true. This, of course, is not the case; old ideas can be bad ideas, and new ideas can be good ideas. We therefore can’t learn anything about the truth of an idea just by considering how old it is.
Anyhoo, do you have enough pictures of confused mid-century honkies on your hard drive? Probably not! Your hard drive needs to be supplemented with the baffled couple from today's ad. Are they any use to you? You can't prove they aren't! Therefore, you need them. Man, if only I made money doing this. Also, 1000 px avatar versions of each, for your online chat service or whatever. You're welcome!