Halliday & Matthiessen (1999: 143):
With many processes of emotion, there is an alternative construal of the emotion as a quality that can be ascribed as an Attribute to a Carrier in a relational clause; and this alternative exists for both the ‘like’ type and the ‘please’ type. Thus I’m afraid of snakes is an ascriptive alternative to the mental I fear snakes; similarly, in the other direction, snakes are scary and snakes scare me. This relational type of alternative exists for some cognitive and desiderative processes, but is much more productive with emotive ones. Analogous attributes in the domain of perception seem always to involve potentiality (visible, audible).