The fourth-preferred, or inferior, function tends to be the least interesting to individuals, and they tend to have even fewer skills associated with it. Development of this function tends to come in late midlife. It can be the source of great stress, or it can be a seed for significant development.
For example, if Thinking were your dominant function, Feeling would be your least-preferred function. You would probably have significantly less interest in and fewer skills with the Feeling function (e.g., attending to harmony in relationships, giving weight to the personal aspects of decision making).
We often call the fourth function the inferior function when it emerges without conscious intention and tries to overpower the dominant and auxiliary. This can lead to a person feeling in the grip of his or her inferior function. The inferior may also manifest under stress, when resources of the dominant and auxiliary are exhausted. When the inferior function manifests in someone's life, that person may say, I don't know what got into me. It often feels like being out of control (outside the conscious ego). The inferior may manifest in negative, immature ways.
For example, Intuition as an inferior Intuition may manifest not as creative possibilities, but rather as worry over every possibility that can go wrong. Sensing may manifest not as attention to details, but rather as an obsession with them.
Was That Really Me by Naomi L. Quenk (CPP, Inc. 2002)
In the Grip by Naomi L. Quenk (CPP, Inc. 2000)