1976 National Parks Training Methods Manual (Eitington)

Source:The Training Methods Manual (Revised by) Julius Eitington, Dept of the Interior, National Parks Service, 1976
Where was it found? HathiTrust: 
Search term: “10% of what we”
What was found? this chart:

It is a generally recognized fact that we retain about:
10% of what we hear
20% of what we read
50% of what we see
90% of what we do