“For the first ten years or so, you would always question whether the decisions were right or wrong, but you have to learn to put things behind you once a decision is made. You can't be wishy-washy about it.”

Source: Snuff

Source: As quoted from CNN's ‘Larry King Live’ in Colin Powell Leaves Many Leadership Lessons For Corporate Executives, Forbes, October 18, 2021

Source: Vanishing Acts

Source: Tracks

Source: The City of Ember

As quoted by John M. Kost http://www.mackinac.org/bio.aspx?ID=104 (25 July 1995) in S. 946, the Information Technology Management Reform Act of 1995: hearing before the Subcommittee on Oversight of Government Management and the District of Columbia of the Committee on Governmental Affairs (1996).
This appears to derive from a 1910 advertisement by writer Alfred Henry Lewis for a forthcoming series of biographical articles about Roosevelt: "All activity, Mr. Roosevelt has often shown that it is better to do the wrong thing than do nothing at all. In politics this last is peculiarly true. The best thing is to do the right thing; the next best is to do the wrong thing; the worst thing of all things is to stand perfectly still". (e.g. in La Follette's Magazine https://books.google.com/books?id=RV4CAAAAIAAJ&pg=PA183&dq=%22best+thing%22+%22right+thing%22+%22worst+thing%22+nothing&hl=en&sa=X&ved=0ahUKEwjNksu-nZrMAhVDy2MKHSl1Df8Q6AEIIzAB#v=onepage&q=%22the%20best%20thing%20is%20to%20do%20the%20right%20thing%22&f=false (28 May 1910)
Disputed

Quoted in: Charles A. Stevenson (2006), SECDEF: The Nearly Impossible Job of Secretary of Defense http://books.google.com/books?id=2NXbS5AG_8QC&pg=PA28, p. 28