I never thought I'd quote cracked.com on my blog, but Geoff Shakespeare did such a good job I couldn't resist (careful, I've cleaned it up a bit here, but the language on the actual article is fairly saucy):
"Albert Einstein said common sense is the collection of prejudices acquired by the age of 18. It is also a result of some pervasive and extremely stupid logical fallacies that have become embedded in the human brain over generations, for one reason or another. These malfunctioning thoughts--several of which you've had already today--are a major cause of everything that's wrong with the world.
#5.The Historian's Fallacy
The problem is, there is something about our brains that just won't let us put ourselves in the other guy's shoes. We're the fat guy on the couch screaming about how LeBron James "choked" because he took that bad shot instead of driving the lane. We're all convinced that, had we been in the same situation, we would have made the right decision; the Titanic wouldn't have sank, the stock market wouldn't have crashed and the PlayStation 3 wouldn't have been priced at $599. The moment we see their mistake in hindsight, we tell ourselves what morons they must have been. The problem, of course, is that when your reaction is to shake your head, laugh and call them dumbasses, it keeps you from learning from their mistakes... To see this happening on a grand scale, just open a history book, or watch the news. George Santayana famously warned in 1905 that, "those who cannot remember the past are condemned to repeat it" and people have spent the last hundred years ignoring him...
#4.The Nirvana Fallacy
The Nirvana Fallacy is when you dismiss anything in the real world because you compare it to an unrealistic, perfect alternative, by which it pales in comparison. It wouldn't be a problem, except it keeps us from getting anything done. For instance... one of the most common reasons we procrastinate is fear that the end result won't live up to the "perfect" idea in our heads. Think about the writer friend of yours who has never actually written anything, because they're "waiting for the right idea" for a book to come along. This is why people wind up living in their parents' basement--waiting for the perfect job, the perfect girl, the perfect friendship--before committing to anything... any incremental improvement on someone else's part is mocked as some kind of deluded hypocrisy, because anything short of perfect is not worth doing, so you might as well do nothing, like them. "Ha! You're drinking a Diet Coke with your hamburger? Like that's really going to make a difference!"
Politicians use this to attack any idea they don't like. "Sure, your plan is helping millions of families in poverty. But I found examples of people abusing it! So we might as well scrap the whole system!"
#3.The Appeal to Probability
Our brains are stupid when it comes to calculating probability. As a result, we all have this fuzzy idea that if something can happen, it probably will. And we think this, while having no idea what "probably" even means. This is why millions of high school kids think they're going play pro sports when they grow up, even though there are only enough available jobs for a tiny fraction of them. When the news says an asteroid may hit the Earth in the next 10 million years, people will watch the skies suddenly sure that an asteroid will hit that day. Hollywood doesn't help us on this one, since every single movie is about the one-in-a-million shot going through. Nobody wants to hear about the underdog who lost the big game 49-0. So after hearing that same story several hundred times, we somehow come away with an unspoken belief that the unlikely underdog always wins. We don't stop to ask why, if that really happens, they are still called the unlikely underdog?
#2.The Regression Fallacy
Human beings are hardwired to see patterns. Seeing links and connections between various stimuli is a big part of how people navigate complex environments. Back in the earlier days of our evolution, it helped us to hunt and find food; today it helps us deal with people, keep track of large amounts of information and figure out just what... is happening on Lost. But misfires in pattern recognition create all sorts of weirdness, particularly in the form of superstition... that's why they call it the Regression Fallacy, because any trend is going to regress back to where it normally is. Crime goes way up in the city, they elect a new mayor, and crime goes down. Wow! This mayor is magic! Or maybe he's secretly Batman! Actually, the crime increase was out of the ordinary and crime was destined to fall back to its normal level. But the mayor--and countless other politicians and gurus--will make an entire career out of exploiting the Regression Fallacy.
Special Pleading is actually when we allow something to be an exception to a rule, for no logical reason. In every day life, people use Special Pleading to make them feel less guilty... When someone else eats the last doughnut, they're a [jerk]; when you or a friend does it, it's because you were really hungry and you've had a bad day and you didn't get any doughnuts the last time. Special Pleading is the lettuce in mankind's hypocrisy salad... You don't need us to point out examples of hypocrisy, from cops who won't write traffic tickets to other cops, to politicians who talk about how important the public school system is while putting their own kids in a exclusive private schools. What's interesting is how everyone excuses it in their own mind. You can't find anyone who simply says, "The rules don't apply to us because we're awesome!" Thanks to Special Pleading, there are elaborate mental gymnastics that happen inside them that eliminate even their feelings of guilt... some of us have held grudges for years, based on actions by someone else that we've forgiven ourselves for doing countless times."