My ongoing list.

I'm amazed that nobody here has referenced the Streisand effect, where pulling something off of a public forum inadvertently makes it a lot more popular.

In America, we wash our eggs to clean any possible infection off of them. This also scrubs a protective layer off of them, which makes it easier for eggs to get infected.

Americans – why do you keep refrigerating your eggs?

- In addition to the Hawaiian's Snail menace, they also decided to import the mongoose to handle their rat problems. As it turns out, the mongoose is diurnal and the rats are nocturnal. The end result was that the mongooses wound up devastating the native (much easier to catch) animal population instead.

- The 18th amendment to the US constitution, otherwise known as "Prohibition". This was intended to decrease the drinking of alcohol. When it was passed in 1918, the city of New York had roughly 800 bars on record. By the time it was repealed the city had an estimated 4000 speakeasies in operation. We still haven't learned that lesson.

- Abstinence only sex ed is targeted at decreasing the number of young adults having sex. There is some question as to whether actually having sex is the problem, or whether the problems caused by sex (e.g., pregnancy and disease) are the problem. If sex itself is a problem then there is no way of telling if the abstinence only education is having an effect due to pervasive self-reporting bias. If the latter is the case, then these programs are a miserable failure. All available studies have determined that the abstinence only approach increases incidence of teen pregnancy and sexually transmitted diseases.

[http://thenationalcampaign.org/resource/emerging-answers-2007%E2%80%94full-report]