A certain style of petach was used by a number of rabbis and yet, was discouraged by the Gemara for concern that people would not tell the truth. This petach took on different forms but the idea was that the chacham would say something like: "Had you known how terrible a sin it is to God to vow, would you have taken this vow?" Since it is unlikely someone would have the audacity to answer 'yes' to this question in front of a chacham, they ruled one cannot use it.  There is a debate between Rava and Abaye regarding whether or not one can use this petach: "Had you known it was like building a bama and sacrificing a sacrifice, would you have vowed?" There is a debate regarding what part of that sentence they disagree about - the bama or the sacrifice? The Gemara brings several statements about the dangers of anger since the assumption is that most people vow in a moment of anger. A story is told of Ulla who witnessed a murder on his travels from Babylonia to Israel. Rabbi Yochanan questions a detail of the story - how one could have gotten angry in Israel and murdered another, as the verse says that God will bring anger outside of Israel. Anger causes one to dismiss the divine presence, causes folly and sin. Is it possible to dissolve a vow/oath if one vowed/swore in the name of God? Most of the amoraim say that it is not, but Rav Nachman rules at the end of the sugya that it is allowed. It is told about Rav Sechora who came to Rabbi Nachman to permit a vow and after Rav Nachman tried all kinds of openings without success, he became angry with Rav Sechora. When Rabbi Sechora left there, he came up with a petach himself that if he had known that it would make Rabbi Nachman angry with him, he would not have made a vow. Another similar story is told about the breaking of a vow of Rabbi Shimon the son of Rebbi.