Always Fulfill a Vow

Miya: You can't promise anything to anyone and if so, you have to make sure you do whatever crosses your lips. You have to make sure people know that you are truthful. You want people to trust you.

Jackson: Bli Neder says to God, "I might do this thing, but if I don't, don't get mad at me." If I say Bli Neder, and I don't do a vow, not everyone will be mad at me.

From Adam: If you lie to someone by not doing something, don't make the offer to do it or say yes to doing it if you think you won't be able to fulfill it. It is better not to do the thing at all, so then you won't let the other person down.

From Wikipedia: Jephthah (pronounced /ˈdʒɛfθə/; Hebrew: יפתח‎ (Yiftāḥ), appears in the Book of Judges as a judge who presided over Israel for a period of six years (Judges 12:7). According to Judges, he lived in Gilead. His father's name is also given as Gilead, and, as his mother is described as a prostitute, this may indicate that his father might have been any of the men of that area.^[1] Jephthah led the Israelites in battle against Ammon and, in exchange for defeating the Ammonites, made a vow to sacrifice whatever would come out of the door of his house first. When his daughter was the first to come out of the house, he immediately regretted the vow, which would require him to sacrifice his daughter to God. Jephthah then carried out his vow (This story is in the Haftorah for Parashah Hukat)