Many people approach problems in similar ways all the time even though they can't be sure they have the best approach or an approach that will even work. Doing this is an example of mental set -- a tendency to approach situations the same way because that way worked in the past. For example, a child may enter a store by pushing a door open. Every time they come to a door after that, the child pushes the door expecting it to open even though many doors only open by pulling. This child has a mental set for opening doors.