A boy adds a get-well message to former South African president Nelson Mandela in Johannesburg (Themba Hadebe/Associated Press)

Nelson Mandela remained in critical condition Monday due to a recurring lung infection for the second day — sobering news about the revered 94-year-old icon who, as Time managing editor Richard Stengel once called him, is “the closest thing the world has to a secular saint.”

Hearing the news about Mandela’s condition, I was reminded of Stengel’s 2008 cover story about Mandela, “The Secrets of Leadership.” On the occasion of Mandela’s 90th birthday, Stengel shared eight lessons of leadership from the great anti-apartheid leader’s life that were culled from new and old interviews with the former South African president. (Stengel worked with Mandela on his autobiography, “Long Walk to Freedom.”)

Though the piece is only available to subscribers — and is worth a read for anyone interested in leadership — a summary of the eight lessons have been shared around the Web. They include aphorisms such as “Quitting is leading too” and “Know your enemy — and learn his favorite sport.”

But some of the best nuggets of wisdom in the piece are quotes from Mandela buried beneath those more familiar leadership ideas. When Mandela was afraid (whether in prison or later in life on a plane making an emergency landing) he admitted to Stengel leaders shouldn’t let other people know: “You must put up a front.” Mandela learned from the tribal king who raised him as a boy that leaders shouldn’t “enter the debate too early,” Stengel writes that Mandela used to say. “It is wise to persuade people to do things and make them think it was their own idea.”

Mandela, of course, had many things to say about leadership over the course of his life, though for many years of it, South Africans were banned from quoting him. Here are a few of the best, with credit to “Nelson Mandela By Himself: The Authorised Book of Quotations”:

“Long speeches, the shaking of fists, the banging of tables and strongly worded resolutions out of touch with the objective conditions do not bring about mass action and can do a great deal of harm to the organisation and the struggle we serve.” (Presidential address to the ANC Transvaal Congress, also known as the “No Easy Walk to Freedom” speech, Transvaal, South Africa, Sept. 21, 1953)

“I had no specific belief except that our cause was just, was very strong and it was winning more and more support.” (Robben Island, Cape Town, South Africa, Feb. 11, 1994)

“Real leaders must be ready to sacrifice all for the freedom of their people.” (Chief Albert Luthuli Centenary Celebrations, Kwadukuza, Kwazulu-Natal, April 25, 1998, South Africa)

“What counts in life is not the mere fact that we have lived. It is what difference we have made to the lives of others that will determine the significance of the life we lead.” (90th birthday celebration of Walter Sisulu, Walter Sisulu Hall, Randburg, Johannesburg, South Africa, May 18, 2002)

“It is never my custom to use words lightly. If twenty-seven years in prison have done anything to us, it was to use the silence of solitude to make us understand how precious words are and how real speech is in its impact on the way people live and die.” (Closing address, 13th International AIDS Conference, Durban, South Africa, July 14, 2000)

Jena McGregor is a columnist for On Leadership.