This is one of the legal maxims of Islamic Jurisprudence regarding the limits one is not supposed to exceed. This principle is defined as:
Darûrah (necessity) that is blockaded by sieges should not exploit Rukhsah. The Dâbit (the controller) here, that limits the Darûrah is a dangerous matter or severe hardship that human beings cannot endure.
...) فَمَنِ اضْطُرَّ غَير بَاغٍ وَلاَ عَادٍ فَلا إِثْمَ عَلَيه (...
(… But if one is forced by necessity without willful disobedience nor transgressing due limits; then, there is no sin on him...) [Surah Al-Baqarah: 173]
Should Rukhsah be restricted by a definite time, a man cannot go beyond that time.
Suppose a person, in order to save his life, was forced to eat a dead animal, he is not allowed to consume more than he actually needs to survive.
A doctor should not look at the private parts of a person except what is necessary.
If someone is starving, and another person, who has more than his immediate needs, refuses to provide the starving person with food, the hungry person has the right to take it by force, and to recompense him later.