How to keep people involved with Wikipedia? was one of the questions put to Jimmy Wales in July 2004, by readers of Slashdot. Wales answered that when there is an edit war or flame war, consider what Wikipedia is all about. Think of a person ‘who lives without clean drinking water, without any proper means of education, and how our work might someday help that person.’ Shortly after that followed the sentence now so prominently known by Wikipedia activists and fans:
Imagine a world in which every single person on the planet is given free access to the sum of all human knowledge.
To some activists, though, this phrasing gives an uneasy feeling, or even more the common call for ‘share your knowledge’. Isn’t the name of your dog or Shakespeare’s digestion on a specific day a part of ‘all human knowledge’? Couldn’t newbies misunderstand the expression and try to contribute unencyclopedic content?
The key word here is ‘sum’: Not all human knowledge but only a sum is the goal, meaning not literally everything but only a summary, a synopsis. Latin works of the middle ages with the title ‘Summa’ were a kind of encyclopedia or a short consumption of a field of knowledge.
Anyway, the expression ‘sum of all human knowledge’ itself can claim no special originality. It is actually very common in the modern history of encyclopedias.
In her PhD thesis ‘Das Streben nach Wissen’, Ulrike Spree refers to the title of a work by George Lillie Craik, from 1830. He wrote that the pursuit of knowledge is different from the pursuit for wealth or fame because it does not need capital or competition. It knows only winners, no losers. 
The title of his work is: ‘The Pursuit of Knowledge Under Difficulties’. Wouldn’t that make a good title for the history of Wikipedia?
 Ulrike Spree: Das Streben nach Wissen. Eine vergleichende Gattungsgeschichte der populären Enzyklopädie in Deutschland und Großbritannien im 19. Jahrhundert, Niemeyer 2000, p. 7.