“Progressive societies outgrow institutions as children outgrow clothes.” - Henry George

Progressive - Going forward or onward; passing successively from one member of a series to the next; proceeding step by step.

Progressive tenses show the continuity of an action instead of its completion. Progressives are often helped by adverbials to show continuity.

Adverbial - A word or group of words functioning as an adverb.

He is always reading books. “Always reading” shows the subject in a state of ongoing action… not complete.