A heuristic is a mental shortcut that helps people to make sense of and simplify things. Without them we'd become buried beneath all the information we are presented with all the time. Two types of heuristics are the representative heuristic, and the availability heuristic. The representativeness heuristic is comprised of judging the probability of something based on how much it resembles something else, or how similar they are. People tend to judge things based on stereotypes. If a person relies too much on the representativeness heuristic, he or she may forget to contemplate the base rate (how common a characteristic or behavior is in the general population). For example, based on just looking at the pictures, which person is likely to read more books?
You might say the guy wearing the glasses, based on your stereotypes.
Another heuristic is the availability heuristic, which incorporates estimating the probability of something based on how easily it comes to your mind. You don't take the time to measure or calculate precise things, but instead estimate based on experiences and what you remember.
Heuristics can show that we can be fooled easily. We should keep in mind that not all heuristics are helpful that they can lead us to faulty conclusions- but many research methods can help us avoid the negative results of misapplying heuristics.
I wonder though, is it possible to control these heuristics? Take the representative heuristic for example, is it possible to not judge someone when you see them? As much a person says they don't judge others, I find it almost impossible to not judge people to some extent- it's almost like asking for someone to have a blank mind when meeting someone until you actually get to know them. I find it only natural to have some thoughts about the person- although you could just focus on positive aspects about the other person.