Practically speaking, I think about this idea when it comes to understanding politics. I feel very limited in my ability to “know my mind” today because of my ignorance of yesterday. (Okay, I have heard tell that the republican party has not always been scary.~) I think of this question when I think about medical history too. My children are adopted and we do not have information on the bio parents, it has added some kinks to caring for them and knowing them fully (biologically speaking).
Inter-personally, as my understanding of human history (in particular those who have been oppressed) my understanding of myself has increased.