 Over the years I have found that it is difficult if not impossible to bring to consciousness of another person the nature of his tacit assumptions when , by some special experiences , I have been made aware of them . This became painfully evident to me in my attempts during the 1950s to convince geneticists that the action of genes had to be and was controlled . It is now equally painful to recognize the fixity of assumptions that many persons hold on the nature of controlling elements in maize and the manners of their operation . One must await the right time for conceptual change . 
