Halliday & Matthiessen (1999: 516-7):
With each type of process, the grammar associates one or two favourite configurations of participants. These usually vary considerably from one process type to another; in English, there is a strong link between the rôle of “Senser” (the one who knows, thinks &c.) in a mental process and the personal pronouns he and she, such that putting it in this rôle (it didn’t believe me, for example) creates an anomaly — we wonder what this “it” could be?