That some accusations are not true, and that some rape never leads to accusations. Most rape is not ever reported, because of the psychological impact it has, and the kind of people clever rapists rape. The rapes that are reported stand in line with a sizable amount of accusations that are false. Sadly, for a jury to tease apart the liars from the valid accusers is hard. It's worse than chance, actually, because rape victims often react to talking about it, especially with the rapist in the room, in a manner which makes them look unconvincing.

What were you implying? That there's some easy answer here?