A more thorough explanation:

The rule of necessity is a legal principle that requires a judge or other official to hear a case, even if they have a bias or conflict of interest. This is because disqualifying them would result in the lack of any competent court or tribunal to hear the case.

For example, if a judge is related to one of the parties in a case, they may have a bias towards that party. However, if there are no other judges available to hear the case, the judge may still be required to hear it under the rule of necessity.

Another example could be if a judge has a financial interest in the outcome of a case. While this would normally disqualify them from hearing the case, if there are no other judges available, the rule of necessity may require them to hear it.

The rule of necessity is important because it ensures that cases can still be heard even in difficult circumstances. However, it is also important to ensure that judges and officials are impartial and unbiased whenever possible.