If it is true that we can only be in one place at a time (contemplate this statement to make sure you truly believe it), then for any given moment we cannot be anywhere other than where we see our body (on the couch in the living room, for example). Though this is such an obvious truth that (most) everyone would agree with, our minds still give us the impression that we can be doing something (right now) that we are not doing, which would likely depend on being in some place other than where we are.
This mental predicament speaks to the “should” thoughts that aimlessly roam around in our head. Do we believe that there is some “other” us that could act on our behalf? If we do not, i.e., if we believe that our single person is the only actual representation of ourself, then what is this familiar feeling (that we could presently be attending to something else) based on? If I am here right now typing these specific words on the computer, and there is no other person that is “me” (even to be typing some other words on the computer) then there is no realistic grounding for these should thoughts. The only grounding would be my physical placement on the ground or furniture I am on, which is thankfully secured by the physical law of gravity.
Look at the surface you are on right now to stay grounded in the knowledge that you truly cannot be in more than one place at a time (or more than one activity at a time). Put that up against any should thought to understand that what it is suggesting is physically impossible.