By and large, the human brain is amazing. We can imagine things that do not exist. We can think into the past, and into future. And at any given moment, our brain is taking in thousands (millions?) of pieces of information from our physical environment. Add another person into the environment, or groups of people, and that information grows exponentially. And yet, we manage to function quite well. That is pretty awesome; it really is.
But, despite that, there are a wide range of biases in human thinking that researchers have discovered. The basic gist behind this research is that what people think is true is often not true. We tend to think that how we see and view things reflects an objective reality, but this is often not the case. To take a quick example, if you ask people if they are better than average at something, pretty much no matter what it is, more than 50% of people will say that they are. One study asked this question about car driving, and found that over 90% of people report thinking they are better than the average driver, and the numbers weren't that far off for people who had been in multiple car accidents!
Perhaps the most interesting human bias (in my opinion at least!) is what Emily Pronin, a psychologist at Princeton University, dubbed "the bias blind spot." Research she and her colleagues have conducted shows that people are largely immune (i.e., "blind") to their own biases. For instance, this research will explain a certain human bias to people, such as hindsight bias (the tendency to exaggerate the extent to which you knew something would happen, once it has happened). It then will ask them how susceptible they are to this bias, as well as how susceptible they think that other people are.