Triad of Days

There are three broad kind of folks, One those live by "yesterday", Two those think in advance of "tomorrow", And three those prefer to stay in"today", There are also minor groups of folks, Those draw upon the three in combinations and permutations, Importance varying in degrees to bygone, present and future, Perhaps ideal are those kinds of fellows, Which treat equally "yesterday" as, Database of events to mark and prevent errors, And "present" as drawing board for "future"events, For past was the present of yesterday and the, future of the day before, The linking triad goes unending.