John doesn't like lemonade, but he likes Sandra's lemonade.
A bias is a prejudice in favor or against something. A contradiction is a combination of ideas or statements of a situation that are opposed to one another.
Bias: John doesn't like lemonade
Contradiction: He likes Sandra's lemonade.
In theory, if John doesn't like lemonade, he shouldn't like Sandra's lemonade either. Since he does, it is a contradiction to his bias.