How important it is to know blood type of the people you know? Despite of the many arguments that the question of blood type can cause stereotype if the person believes that there is a correlation between blood type and personality, many Japanese, perhaps due to living a society with less multicultural background, still consider blood type as a key factor to understand differences in behavior and social characteristics.
There was already research on blood type and personality correlation in Japan many decades ago, however at least in the past three to four years, blood type has again become a hit topic of conversation among friends, members of circle/group, family and this is most likely caused by a series of best seller books on blood type and personality. The success of this book was even discussed in our national TV channel, NHK in 2008.
Overseas, there no substantial findings that suggest blood type and personality are related. However, if you happen to be asked by a Japanese, what is your blood type, would you not care to how the person may perceive your personality based on your answer.
Now, take it easy and enjoy this video: