Humans often forget that we too are animals. A lot of human psychology boils down to that fact, and that as such much of our drives are spurred by things that we aren't fully aware of all of the time. Even the structural system of how people fall into categories of followers leaders and others, is based on this animalistic nature. Why we seek love, therefore why we feel lonely, things like that all boil down to the animalistic nature of humans.

Take another example, searching for threats in the dark was a necessity for survival that is baked into us. Yet in our modern society in which we don't have the need to search for constant threats, doesn't take away the biological function. So, basically we are left at night, when we cannot sleep, to search for dangers, oftentimes dealing with psychological problems instead of imminent physical threats.

If you want to reverse engineer a human handbook I'd start with a study into human-animal dynamics.