In Japan, many believe your blood type tells of your personality and relationship compatibility. Masahiko Nomi, a Japanese journalist, researched the relationship between the four blood types. He tracked the difference of personalities, and published several books in the 1970s, which were a huge success. Nomi’s blood-type theory of personality was rapidly accepted throughout Japan, and today, many this a strong strategic tool in learning the personality of others and building effective human relations.