"A blade of grass is a commonplace on Earth; it would be a miracle on Mars. Our descendants on Mars will know the value of a patch of green. And if a blade of grass is priceless, what is the value of a human being?" -- Carl Sagan (b. 1934-11-09, 1996-12-20), Pale Blue Dot: A Vision of the Human Future in Space, 1994
"If we are to send people, it must be for a very good reason - and with a realistic understanding that almost certainly we will lose lives. Astronauts and Cosmonauts have always understood this. Nevertheless, there has been and will be no shortage of volunteers." -- ibid.
[1967-01-27: Apollo I fire kills Grissom, White, and Chaffe]