Halliday & Matthiessen (1999: 138):
In contrast, perceptive and emotive types of sensing cannot project ideas into existence. That is, ideas do not arise as a result as a result of someone seeing, hearing, rejoicing, worrying, grieving or the like. However, these two types of sensing may accommodate pre-existing projections, i.e. facts, for instance:It assures me [[that I am as I think myself to be, that I am fixed, concrete]].
I was impressed, more or less at that point, by an intuition [[that he possessed a measure of sincerity the like of which I had never encountered]].
We heard [[that you kindly let rooms for gentlemen]].Thus ‘that I am fixed, concrete’ is construed as something already projected (hence we could add assures me of the fact that) and this fact brings about the emotion of assurance.