A thing which is permissible by reason of the existence of some excuse thereof, ceases to be permissible with the disappearance of that excuse. When a prohibition is removed, the thing to which such prohibition attaches reverts to its former status of legality. An injury cannot be removed by the commission of a similar injury. A private injury is tolerated in order to ward off a public injury. The prohibition from practice of an incompetent physician is derived from this principle.
Severe injury is removed by lesser injury.
In the presence of two evils, the greater is avoided by the commission of the lesser. The lesser of the two evils is preferred. Repelling an evil is preferable to securing a benefit. Injury is removed as far as possible. Any want, whether of a public or private nature, is so dealt with as to meet the exigencies of the case.