What is it?
I/R Theory is an idea David Sandler espoused that effectively separates the various roles we accept and perform in our lives from the very core of our self which cannot be defined by any given role other than human being.
Why is it important?
When seeking to get along with other people, or build our own self-esteem, it is useful to strip away all roles to acknowledge the basic human value each of us possess. On a scale of 1 to 10 with 1 being low, and 10 being high, devoid of any roles we are all a 10. When we see others as the 10's they really are, it makes it easier for us to find something in them to like. When we see ourselves as the 10 we really are, we open up the possibility of achieving our maximum performance in any of our given roles.
When people see themselves as less than a 10, a 5 for example, it limits their potential to perform at a high level in their roles because no one can exceed "who they really believe they are" in any of their chosen roles. Much like self-image and self-esteem this is a way to open up the value we place on ourselves and others by stripping away what are sometimes negative aspects of a person - such as being a bad __________. (Fill in the blank with a role of your choice, ie. dad, worker, housekeeper, friend etc.) We are still a 10 at our core being.