Let us discuss the word אתמול - Yesterday (but let's do it today).
This word appears in consecutive roshei teivos one time in all of Tanach!! (No occurrences at all in sofei teivos.) And the lone occurrence is in - you guessed it - the Parsha that we read yesterday - Parshat Ki Teitzei.
In Parshat Ki Teitzei, in the passage that deals with lost possessions, we have the pasuk (Devarim 22:3):
וכן תעשה לכל אבדת אחיך אשר תאבד ממנו ומצאתה לא תוכל להתעלם
Rav Aharonovsky, ShLiT"a wants to suggest that the most precious thing that one can lose is אתמול - Yesterday, because this is one thing that one can never get back.
He goes so far as to quote the famous verse that has been attributed to one of the rishonim:
אדם דואג על איבוד דמיו
ואינו דואג על איבוד ימיו
דמיו אינם עוזרים
וימיו אינם חוזרים
A man will cry for money misspent,
But for days that are gone he does not lament.
His wealth will not help at the time he will grieve,
And a day that has passed he can never retrieve.