We are all born ignorant, but one must work hard to remain stupid.

Benjamin Franklin (1706-1790) American statesman, scientist, philosopher, aphorist

(Spurious)

Attributions of this to Franklin cannot be found in print before 1999. Search of his papers and various other sources do not find it.

Franklin did write at times about ignorance (e.g.), and in fact did write this similar aphorism:

Being ignorant is not so much a Shame, as being unwilling to learn.
 

But he does not seem to have used the phrasing above.

For more discussion about this quote:

• PolitiFact | No, Benjamin Franklin did not say ‘We are all born ignorant but one must work hard to remain stupid’
• Barry Popik: "We are all born ignorant, but one must work hard to…
• american english - Quotation ascribed to Benjamin Franklin, "We are all born ignorant, but one must work hard to remain stupid." - English Language & Usage Stack Exchange