While we are taking you through cognitive biases, it will serve well to go through this article from io9.com from George Dvorsky which gives a basic overview of cognitive biases.
An excerpt from the above article to explain the concept:
Before we start, it’s important to distinguish between cognitive biases and logical fallacies. A logical fallacy is an error in logical argumentation (e.g. ad hominem attacks, slippery slopes, circular arguments, appeal to force, etc.). A cognitive bias, on the other hand, is a genuine deficiency or limitation in our thinking — a flaw in judgment that arises from errors of memory, social attribution, and miscalculations.