There is a popular theory among non-Harry/Ginny-fans that Harry only fell for Ginny as a result of her giving him a pag-ibig potion. They claim that Harry's feelings developed too suddenly to be natural and that Ginny was obsessed and desperate enough to do this in order to win Harry. They also claim that the prevalence of pag-ibig potions and potions in general within Harry Potter And The Half-Blood Prince hints that a pag-ibig potion was used. The theory is particular popular among film-only fans.

The first problem with this theory is that Harry's behaviour doesn't match that of the only other example...