Why would that knowledge be a problem? Do cars stop working when you know how they work?

That isn't a good analogy. Many humans have trouble actively trying to change their own emotional or belief states. The analogy that might be more appropriate is trying to deceive oneself into believing a false statement. I don't think that the analogy quite holds either liking someone is much closer to an emotional setting. It is thus closer to someone say deliberately conditioning themselves in some way. Even if you know, you are doing it, you can still use fairly primitive conditioning. But Nanani's question is one that still requires some response: the car analogy is not sufficient.