If Blood O can be mixed with Blood A i.e O donating to A, then why can't A be mixed with O i.e. A donating to O. Basically If we can put O into A then we must is able to put A into O. But we know the second case isn't possible. Why so? And if I kind of reframe my question then it goes as when Blood O is donated to A then why doesn't the antibody A in Blood O coagulate with Antigen A in Blood A?

If Blood O can be mixed with Blood A i.e O donating to A, then why can

1.	If Blood O can be mixed with Blood A i.e O donating to A, then why can't A be mixed with O i.e. A donating to O. Basically If we can put O into A then we must is able to put A into O. But we know the second case isn't possible. Why so? And if I kind of reframe my question then it goes as when Blood O is donated to A then why doesn't the antibody A in Blood O coagulate with Antigen A in Blood A?
Answer» If Blood O can be mixed with Blood A i.e O donating to A, then why can't A be mixed with O i.e. A donating to O. Basically If we can put O into A then we must is able to put A into O. But we know the second case isn't possible. Why so? And if I kind of reframe my question then it goes as when Blood O is donated to A then why doesn't the antibody A in Blood O coagulate with Antigen A in Blood A?