This morning, I had a bunch of high school students visiting my lab. I explained to them that I study decision-making in the fruit fly Drosophila, unlikely as that may seem to them. In my 10min presentation, I pointed out to them that - like with people - you need to put flies in the right situation to be able to study them making choices. As an example of the wrong situation I mentioned the fly constantly banging its head against the window.
After I told them how we study decision-making in flies, one of them asks me if the punishment the flies receive from banging their heads against the window is simply too weak to make them decide it's not worth trying any more. I answered that I thought it's more likely that the light stimulus is so dominating their behavior that there are no other choices the fly could possibly make. I likened this to them being both hungry and thirsty during a test: they would only be able to think about food and drink and not be able to focus on the test.

After the students were gone, I came across this letter to Nature and then the discussion about it at Pharyngula. Talking about this over lunch with some colleagues, I realized how right Indrani Ganguly-Fitzgerald was when she said: I thought that for some people, their religion really is pretty much like sunlight for flies: It is so dominant that no matter how much it would help them to turn around, they can't help but keep bumping their heads into the glass.