How can numerous vows be fulfilled, and what is the ruling on the inability to adhere to them, such as vowing not to eat for a week and then failing to fulfill it, or swearing on the Qur'an to do something and then not doing it?

The vow that must be fulfilled is one related to a recommended act, such as voluntary fasting, charity, or reciting the Qur’an. If you do not fulfill it, then expiation is due upon you. As for vows concerning permissible acts, such as vowing to sit or stand or not to eat or to remain silent, nothing is binding upon the one who made the vow, neither fulfillment nor expiation. Al-Qurtubi and Ibn Hazm have transmitted scholarly consensus that it is not binding.