Blood typing

Why do so many people believe the "Blood typing"? I dare say that there is no scientific proof for that. Even university-graduates and those who are involved in science often say things like "I'm not so meticulous because my blood type is O." and "You two may not have a good match because you are A and B".

I'm not sure if this kind of idea is typical for Japanese or not but anyway it seems too childish. I guess it is popular because stereotyping others makes it easier to "understand" them.

Once my teacher of biology told us that blood typing is like a religion. "Some people believe it, and others do not." It was when we studied the red corpuscle and antigen on it, so the blood typing seemed untrue. IF you could classify people into four types according to the blood type, there would never have been misunderstandings or arguments.