What are the legitimate excuses for breaking a vow? Thank you.

Vows are divided into two categories: a vow that does not require fulfillment, such as a "vow of obstinacy and anger" (nathr al-lajaj wa al-ghadab) and a permissible vow (nathr al-mubah), in which the person making the vow has the choice between fulfilling it or offering an expiation for an oath (kaffarat al-yamin). The second category is a vow that must be fulfilled, which is a "vow of righteousness and obedience" (nathr al-tabarrur wa al-ta'ah), whether it is conditional or not. If this vow is made, it becomes obligatory to fulfill it, as the Prophet, peace and blessings be upon him, said: "Whoever vows to obey Allah, let him obey Him." It is not permissible to abandon it except in cases of inability. If one is unable to fulfill a vow of obedience, then if there is a substitute for it, he should perform the substitute. If there is no substitute, it remains an obligation upon him.