"And it came to pass [in Hebrew, "vayehi"] in the days of Ahasuerus." (Esther 1:1)

The Talmud states that "vayehi" is an expression of pain and trouble. (Megilla 10b) Rabbi Alkabetz explains that at the basic level of interpretation, "vayehi" consists of the elements "vay" and "hi", both connoting sadness (similar to our "hey" and "oy vey", or "woe"). In addition, the "va-" grammatical tense is used to switch a future action ("yehi") into a past occurrence. This is not happy because the past tense indicates entropy and lack of present or potential existence.

On a deeper level, he explains that the two letters vav and yud of G‑d's name Havayah represent the active principle (the "masculine" flow), whereas the letter "hei" hints to the attribute of severity. Therefore, the word "vayehi", in which the hei (i.e. severity) precedes the final yud, gives a sense of limiting divine flow, and indicates divine judgments overruling the attribute of kindness.