It probably goes without saying that what made you happy in elementary school (cough, Darien from Sailor Moon) isn't what makes you happy now (sorry, Darien, I moved on). On the surface, this may seem like a simple matter of your tastes changing. But, social psychologist Jennifer Aaker, PhD, argues it's a bit deeper than that. Your happiness is determined more by the motivating forces that drive you — think discovery, achievements, or balance — than it is by your likes and dislikes. "[Our] meaning of happiness appears to shift in systematic ways every five or 10 years," she explains in the video below, which was prepared for the Future of Storytelling's 2015 summit. Dr. Aaker clarifies that, rather than rewriting our definition of happiness every decade, the definition actually evolves. She refers to these stages as chapters, and the average human life can be broken down into five of them. In your childhood and teen years, you typically find happiness through discovery and excitement (yes, exactly, like the excitement and novelty of Sailor Moon, thank you). You seek out things that help you understand the world around you, which is still pretty new to you. As you enter your 20s and 30s, Dr. Aaker explains, you likely progress through the second and third chapters: pursuit and balance. Succeeding and feeling validated by others motivates you early on, and then stability (settling down, maintaining your personal health) may start to take priority. In other words, you'll find that practicality becomes more pleasing between chapters two and three. The closer you get to middle age, your sources of happiness will probably become much more, well, selfless. Caring for others will take precedence over the pursuit of personal accomplishment, and reflecting on what you already have will make you especially happy. Dr. Aaker explains that by chapter five, you will most likely seek out a much more tranquil kind of happiness, compared to the excitement you found the most gratifying in your youth. She suggests that older people derive joy from feeling content and connected. Dr. Aaker also describes her research on the subject of happiness and its stimuli, which she conducted with colleagues Cassie Mogilner and Sep Kamvar. Check out the full video to hear about their findings on other ways age and happiness work off of each other — and how these chapters vary from person to person. The Future of Storytelling is an organization dedicated to understanding how technology and science interact with human nature and communication. You can browse the rest of this year's summit videos here.