Mark Twain's learning about people

"During the two or two and a half years of my apprenticeship, I served under many pilots, and had experience of many kinds of steamboatmen and many varieties of steamboats; for it was not always convenient for Mr. Bixby to have me with him, and in such cases he sent me with somebody else.  I am to this day profiting somewhat by that experience; for in that brief, sharp schooling, I got personally and familiarly acquainted with about all the different types of human nature that are to be found in fiction, biography, or history.  The fact is daily borne in upon me, that the average shore-employment requires as much as forty years to equip a man with this sort of an education.  When I say I am still profiting by this thing, I do not mean that it has constituted me a judge of men--no, it has not done that; for judges of men are born, not made.  My profit is various in kind and degree; but the feature of it which I value most is the zest which that early experience has given to my later reading.  When I find a well-drawn character in fiction or biography, I generally take a warm personal interest in him, for the reason that I have known him before--met him on the river."  from Life on the Mississippi

--The pilots and characters that Twain describes in this book are indeed "well-drawn" and full of color.