Knowledge

It's estimated that medical knowledge, for example, doubles every seven years, and scientific knowledge doubles every twenty years.

The total written knowledge in the world is said to have doubled between 1450 and 1750, and then to have doubled again between 1750 and 1900. 

Between 1900 and 1950, human knowledge doubled once more, and then again from 1950 to 1975.

Now, it is believed to double every 900 days. By the year 2020, global knowledge is predicted to double every 72 days.

plain truth = schooling never ends; education is never finished.