The scene: I'm sitting in a GO bus, putting on my seabands in the hope of warding off motion sickness.
Guy next to me: "What are those things?"
Me: "They prevent carsickness. I put them on my wrists, and this sticky-outy plastic bit presses into an acupressure point that relieves nausea."
Guy next to me: "Those are a scam, you know! They're totally unproven, they don't do anything at all, it's all in your head!"
Now, it is true that I can't say for certain that the seabands work. I've never thrown up while wearing them, but I also haven't thrown up on many many occasions when I wasn't wearing them.
But this guy was about to sit next to me for a long bus ride. If it were true that the anti-nausea measures I'm taking are entirely psychosomatic, he would have an immediate personal investment in my believing in them! Why would you try to convince the person next to you on a long bus ride that their psychosomatic anti-carsickness measures are all in their head?