According to Transactional Analysis each of us tends to act from three mental or "ego" states of child, parent, or adult. When our inner child is activated we think, feel, and act as we did as a child. Our parental self is built on the thoughts, feelings, and actions learned from our parents. The adult position is used for reasoning and to gather, evaluate, and store information. Adult feelings, attitudes, and behaviors tend to reflect current reality so are not affected by childhood or parental issues.
Knowing which state we or others are working from can enhance interactions and relationships considerably or signals can get crossed and communications fractured and failing. For example someone who is unreasonably stubborn or emotional may be expressing their inner child and difficult to handle. Similarly, if someone is overly bossy or critical they may be playing out their parents roles unconsciously. This dynamic was first explored in Transactional Analysis (Wicki). If you would like to learn more, check out this Wikipedia on T.A. or this popular (but older) book: Born to Win.
As for the adult, the main concern is to transform experience into information then process it as the basis for present or future action. The adult is organized, adapts well, and is intelligent and experienced, and deals objectively and appropriately with things as they are. so collects and organizes information to predict results of actions and make wise decisions. Yet even the adult needs good information to make good decisions. Therefore the adults reliance on objective information avoids mistakes and increases chances of success.
But if the adult is so smart, why not live from that position exclusively? The problem is the adult can be a bit too rational and centered so occasionally also become unfeeling, robotic, and even boring. The best adults also incorporate the joyous, emotional, creative, and other positive aspects of the inner child. Also the positive inner parent can be very helpful as a teacher, guide. and mentor through life's many challenges, complexities, and wonders.
When there is conflict and difficulty in interactions between child and parent states in ourselves or with others, the adult can referee and create compromises for better decisions and actions. One must, however, have a good understanding of parent and child ego states to achieve the best results. Also keep in mind that our own and others mental state can be contaminated by the one of the others or shift between them at any time. With the adult ego state positioned as executive the child and parent states are free to express themselves appropriately.
That is where the magic happens, as we tone down negative beliefs, feelings, and behaviors we learned growing up that play out unconsciously until we bring them into awareness so that the best of our inner child and parent can come together to express ourselves in whatever way is needed in the moment to live authentically, fully, and happily through-out our lives whatever comes our way. There will be losses we must grieve and mourn, but also joys, successes, and achievements to enjoy, share, and celebrate.