In psychology, sets are expectations about experiences that make individuals more likely to behave in a certain way based on past experiences. These expectations make individuals more likely to notice or perceive certain types of information.
One example is a perceptual set which is an expectation to see or perceive something based on prior experience. Another example is a mental set which is the tendency for individuals to approach problems using only solutions that have worked in the past.
An example of a mental set would be attempting to fix a friend's computer by using methods that have always worked on yours without considering their computer is a different brand and has a different operating system that doesn't work the same way.