When I was a kid, school dining halls had big posters telling you to drink milk. They were paid for by Valio, a company that processes almost all of the milk in Finland. The posters said that you have to drink milk for healthy bones, hair and nails – if you didn’t you’d grow up bald and broken-boned (no, seriously, they had illustrations of this).
At the time I believed the posters because I believed pretty much everything I was told in school. I didn’t drink milk though (don’t like the taste), but felt vaguely dodgy for it. I did slightly wonder how people get by in the parts of the world where they don’t drink milk (or what humans did before they domesticated milkable animals), but I never made the connection that the posters advertising milk were advertisments. In retrospect, it seems almost unbelievable that even the name of the milk company on the posters didn’t clue me in – and I thought I was a smart kid!
Some of the other useless advice I got was to avoid drugs and unprotected sex, warnings that seemed more like a cruel joke than anything else.