Somebody flips a coin 100 times. It's come up heads each time. What are the odds it comes up heads on the 101st throw? If you're doing a probability problem, the answer is 50%.
If the coin is fair, the answer is 50%... but what are the odds that the coin is fair, given that it's come up heads 100 times?
The chapter on judgment under uncertainty in the (excellent) new Oxford Handbook of Cognitive Psychology has a handy little section on recent critiques of the "heuristics and biases" tradition. It also discusses problems with the somewhat-competing "fast and frugal heuristics" school of thought, but for now let me just quote the section on heuristics and biases (pp. 608-609):
My thanks to MIRI intern Stephen Barnes for transcribing this text.