Ike drafted both success and failure letters before the invasion.  It was not a lack of faith that had him draw it up but a sense of preparedness.  Most projections had the D-day invasion with at best a 50-50 chance of succeeding.  It is amazingly difficult and costly to assault a defended beachhead.  The drafting of a failure letter was simple prudence.  What is significant is that Ike takes all responsibility for failure on his own shoulders.