If you are eating a wonderful dinner, listening to music, or talking to your wife and you are in your head fantasizing
about your upcoming vacation, then you are really not enjoying the dinner or music and you are not giving your wife the attention that she deserves. Mind like water (having an empty head so you can be present to what is happening and respond appropriately) comes from eastern beliefs. Getting there is not free/easy although emptying your head i.e. writing incompletions down does facilitate this (MUCH more is required to really accomplish this).
This topic is really outside GTD, though GTD can be helpful toward this.
Not sure if that will make any sense.