Megillas Esther 1:2 “Vayihi Bimei Achachveirosh” – “And it was in the days of Achashveirosh”
(Esther Rabba, Psichtos, 11) Every place when it says “Vayihi” – it connotes sorrow. What is the sorrow that is suggested at the beginning of Megillas Esther? Haman HaRasha began his ruse to destroy the Jewish people.
Adding on to the above Midrash, the Nachlas Dovid points out that every place it says, “ViHaya” it is a connotation of happiness that is to come.
The root of the word Vayihi = Yihi (will be) however is clearly connected with something that is to happen in the future. By simply adding a vav at the beginning of the word we change the word from future tense to past tense – [Va]Yihi.
The same has proven to be true with the word ViHaya. By simply adding a vav infront of the word haya (it was) the word becomes – [Vi]Haya, which has a connotation towards the future. (“Vihaya Biacharis Ayamim” – “And it will be in the end of days”)
Now that we understand that the added Vav entirely switches the meaning of the word. We can begin to understand as to why the word Vayihi = sorrow and why Vihaya = happiness.
One who is left in sorrow wishes to switch the circumstances of their present situation to the way that it used to be in the past. On the flipside, one who is presently in a state of happiness wishes that their happiness and good fortune will stick with them into the future.