Apparently you don't understand the quote - and don't know who said it - and, got the quote wrong as well!
The quote refers to no man being able to live apart from mankind.
It wasn't Teddy Roosevelt who said it - it was John Donne, in his poem 'No Man is an Island'
No man is an island entire of itself; every man
is a piece of the continent, a part of the main;
if a clod be washed away by the sea, Europe
is the less, as well as if a promontory were, as
well as any manner of thy friends or of thine
own were; any man's death diminishes me,
because I am involved in mankind.
And therefore never send to know for whom
the bell tolls; it tolls for thee.
It was made very famous by Dr. Martin Luther King Jr. June 1965, Oberlin Ohio
"Any man's death diminishes me, for I am a part of mankind" - powerful stuff!
https://www.youtube.com/watch?v=fpw5UjybLh0