The Formula to Friendship, Written Down and Explained

Dr. Jack Schafer, a retired FBI agent, introduced the Friendship Formula in the book, The Like Switch. Schafer was assigned to the FBI’s National Security Behavioral Analysis Program, and as an expert on human behavior and interactions he found that
Friendship is formed by 4 elements. Proximity, referring to the distance between you and someone else. Frequency and Duration, meaning the number of times you see the other person and how long you spend with them.