Zero one infinity rule

The Zero one or infinity (ZOI) rule is a rule of thumb in software design originated by early computing pioneer Willem van der Poel. It suggests that arbitrary limits on the number of instances of a particular entity should not be allowed. Specifically, an entity should either be forbidden entirely, one should be allowed, or any number (presumably, to the limit of available storage) of them should be allowed. It should not be the software that puts a hard limit on the number of instances of the entity.