One of the methods that a sage makes use of when working with someone who wants to have his neder annulled is called haratah – regret. The sage may point out unintended consequences of the vow and ask the person whether he would have taken the vow had he realized that this is what would develop from it. Responding in the affirmative – i.e. stating that he never would have made such a neder had he realized that – allows the sage to permit the neder.
The Gemara relates a series of cases where this was done. One example of such a situation is the story of Rabbi Yannai Sabba’s grandson who approached his grandfather and asked him to annul his vow. Rabbi Yannai Sabba asked him whether he would have taken a neder had he realized that his pinekas – in heaven – would be opened. The grandson replied that he would not have done so, and Rabbi Yannai Sabba permitted the neder.
According to the Rosh, the concern that the pinkas of a person who made a vow would be opened (i.e., his actions examined) stems from the fact that he violated the advice of the Sages who discouraged taking vows in general. The Talmud Yerushalmi explains it as a criticism that a person is looking to add more prohibitions to himself than are required by the Torah, for are not the Torah ‘s prohibitions sufficient? The Midrash Tanḥuma claims that even Ya’akov Avinu was punished for taking a neder, and that the incident with Dina and Shekhem was the result of his vow.