This is a very general construction abstracting over a range of more specific uses. In this construction, a person or entity (the Agent) is put in relation with a particular event or situation (a Fact), expressed as a clause optionally introduced by 'that'. The nature of this relation depends on the verb that is used in the construction: communication (the Agent verbally expresses the Fact as a message: say, claim), cognition (the Agent has the Fact in mind: think, realise), emotion (the Agent has a particular emotional reaction to the Fact: like, fear), and several others.