ASPEN, Colo. — There’s a tradition in the White House: Outgoing presidents leave a private note for their successors.

Six former Food and Drug Administration commissioners were asked over the weekend to give some verbal — and public — advice to the newish commissioner, Dr. Robert Califf, whose appointment was confirmed in late February. The six were on a panel at the Aspen Ideas Festival’s Spotlight Health conference.

Califf was in the audience, soaking up the wisdom and good wishes, but declined to talk afterward about what he took away from their comments.

Moderator Jackie Judd, a special correspondent for “PBS NewsHour,” asked Drs. Margaret Hamburg, Andrew von Eschenbach, Mark McClellan, Jane Henney, David Kessler, and Frank Young, in reverse order of their service, what they would say to Califf in a note that began, “The most important thing you can do is …”

Margaret Hamburg (May 2009 – April 2015)

Hamburg: “I think I said to him: Develop a thick skin and keep smiling.”

Andrew von Eschenbach (Dec. 2006 – Jan. 2009)

Von Eschenbach: “… Drive critical thinking. The problem with that is you often will be thought of as criticizing, when in fact it isn’t criticizing, it’s driving the ability to think critically about what we’re doing and how we can do it better.”

Mark McClellan (Nov. 2002 – March 2004)

McClellan: “Protect and support the staff. You will get the big ideas accomplished if they feel like they can take the science to the next level, if they get the resources they need to do their job and if when … there is a controversial issue, you, the commissioner, are out in front, taking the heat. Probably your most important job for protecting the staff is being the heat shield. And let them do the science, let them do the right thing to advance public health.”

Jane Henney (Dec. 1998 – Jan. 2001)

Henney: “When I became commissioner … I invited all the previous commissioners into the office … and I went around and asked them what advice they would give me. And I remember Charlie Edwards’s advice the most. [Edwards was FDA commissioner from 1969 to 1973.] Charlie looked at me, cocked his head, and he said, ‘You’ve got the job. Do it the way you believe is right and you’ll be fine.’ So Rob, there’s to you.”

David Kessler (Nov. 1990 – Feb. 1997)

Kessler: “About six, eight months into the job it sort of hit me. Because I had studied the agency. I’d taught about food and drug law … and all the regulatory processes and all of a sudden it dawned on me that those things were important but they were secondary. The real gift you’re given when you are commissioner is you can have an enormous impact on the public health. And that has to be kept paramount.”

Frank Young (July 1984 – Dec. 1989)

Young: “At all times protect the public health. Tell the truth. Be absolutely honest. And be incredibly courageous.”