The Nobel Prize, she says, is both an honor and a challenge -- to go further, push harder and spread her movement farther afield in Africa, where she believes traditional forms of development so often have failed.
It is a point she made as a challenge during a speech she delivered Monday at the United Nations, where a gathering to honor her erupted in an ovation as she entered one of the U.N.'s cavernous chambers.
She is one of their own, a child of the United Nations. Her movement received an early and crucial boost from a U.N. grant, so she has come to offer thanks. But also to challenge the conventional wisdom on development aid, which often targets symptoms of a nation's problems rather than causes.
She reminds the U.N. group of the stool with three legs, which she likens to the concepts of peace, good governance and sustainable management of resources.
"Anybody trying to sit on a stool that has only two legs knows only too well, you will fall. And that is why often development agencies that do not see development requiring these three things, these three pillars, they can put all the money they want into the society but there will be no development.
"And that is part of the reason why in many regions we have not been moving forward, in many cases we have been moving backward."
One small moment can change the course of someone's life. One act of foresight, one act of kindness, one bending of convention and, voilà, life is suddenly different.
When she was a girl, Maathai's eldest brother, Ndiritu Muta, asked their parents one day, "Why doesn't she go to school too?"
"Let her also go to school," she heard her brother saying. "Why isn't she going to school with us?"
Traditionally, most rural African girls, especially in her generation, were not educated. Their role was to do chores and prepare for the husband and children they would nurture one day.
But Maathai's parents relented. They enrolled her in a primary school, then a missionary convent high school. And when she graduated, she became one of hundreds of African students who went to study in the United States under a program designed to prepare a new generation of leaders for postcolonial Africa.
In 1960, she flew on an airplane for the first time. In New York she rode an escalator for the first time (and lost her shoe getting off). Then she took a Greyhound bus with two other Kenyan students to Mount St. Scholastica College in Atchison, Kan., which today is known as Benedictine College.
College life was full and rich, and her travels in the United States during that time were filled with wonderments.
She saw the great Mississippi River, which she had read about in geography classes back in Kenya, how it meant so much to U.S. history and commerce. In her mind it had loomed as a mighty, mighty force of nature.