Such stuff may have too much serious belief around especially in Asia that they even believe blood type has any effect on personality but the reality is such ideas are BS. There is no way it can effect personality whatsoever because personality is because of your active genes, current chemical reactions patterns and your memory and memory has the greatest effect on personality.
However how BS "personality typing" stuff can effect personality is just in the way the person learns about them and believe in it enough to "mentally program" themselves to befit themselves to these personality profile they believe they should be like "I'm Cancer so I should be shy" and people misunderstand each other and cannot see how others trully are because they say "He is too shy because he is Cancer" when there is no real sign of him to be a shy person at all lolol. But the danger here is believing about them despite you don't intentionally follow these ideas. People can subconsciously follow these BS ideas without being aware of just because in deep down they believe "I'm Cancer so I should be shy" mentality. That's why knowledge and beliefs can be dangerous for society and therefore society should be protected from believing in BS by deleting BS from the face of Earth even if it means we have to burn down libraries!!!!!

lol
Another thing, due to how personality greatly affected by so much different variations of genes people cannot be put into the same label for personality typing especially because no person is one thing let alone few things. From a scientific POV even a middle school science class should be enough to make people learn why such stuff is BS lol.
The greatest reason of it is good old method of "saying something vague in generalized way so either way it will fit to every person" thing. Every zodiac type can be shy but they say Cancers are shy so naturally there will be tons of Cancers who are shy. Being shy is a general human thingy. But they also say lots of broad stuff.
Same shit as fortune reading and Astrology BS. They say "hmm Mars will get near to Earth therefore damn Cancers will have relationship problems in 3 months" which is dude everyone experiences such stuff. Shit is too BS scam lol.