3. An old legend says that people are born with an invisible string tied to one of their fingers. This is linked to one other person on the Earth, with whom they are destined to be with. This old legend is highly unlikely to be true, but it illustrates that humans are not meant to be alone, that they are meant to be with someone else.
'Humans are the only creatures on Earth whose young are utterly helpless for years, and heavily dependent on adult care for more than a decade' (The Happiness Hypothesis). This is because humans, unlike other primates, are born before their brains have reached full development. 3 million years ago, humans began to be born before their brain was fully developed. This allowed for the brain to continue growing after being born. This allows for a more massive, evolved brain. The infants could not be born with this large brain because there was a limit to how big a head that a female could deliver while still maintaining a narrow pelvis to walk bipedally.
This period of brain development leads to strong bonds being formed while still young. These bonds formed at such a young age are similar to the bonds that people form with their romantic partners as adults. The humans still try to form bonds that they can rely on, just like when they were young, developing children. The legend of the invisible string is like the bond that all adults form with one another, looking for that person that they can rely on.