In psychology and cognition, unpacking refers to the process of fleshing out details that are usually compressed for efficiency in our imagination or quick reasoning.
Our imaginations are inherently limited; they can’t include all details at once. (Otherwise you run into Borges’ map problem—if you want a map that contains all the details of the territory that it’s supposed to represent, then the map has to be the size of the territory itself.) Unpacking is a way of re-inflating all the little particulars that had to be flattened so your imagination could produce a quick preview of the future, like turning a napkin sketch into a blueprint.
Related: Metacognition, Staring into the Abyss