What a wonderful quote from Barack Obama:
"when this recession began, many families sat around their kitchen table and tried to figure out where they could cut back. That is a completely responsible and understandable reaction. But if every family ... cuts back, then no one is spending any money, which means there are more layoffs, and the economy gets even worse. That's why the government has to step in and temporarily boost spending in order to stimulate demand"
As an encapsulation of what I'd call "naive Keynesianism" it's perfect. As a practical policy tool it's horrible. There's a booming industry in reinterpreting the conventional wisdom about the Great Depression, and as evidence for why this is necessary consider Johann Hari (someone who doesn't let complete ignorance of a discipline prevent him from pontificating):
We can see that the Great Depression got much worse when governments took the Cameron route, and was ended by a giant programme of debt-funded government spending."