There are two kinds of men who never amount to much: those who cannot do what they are told and those who can do nothing else.
Those who know, do. Those that understand, teach.
Those that can, do. Those that can't, complain.
It is those who can see the invisible that can do the impossible.
Those who can't do, teach. And those who can't teach, teach gym.
Those honor nature well, who teach that she can speak on everything.
The authority of those who teach is often an obstacle to those who want to learn.
It's those who lie outside ordinary experience who have the most to teach us.
Those who can kill themselves do, and those who can’t, teach philosophy.
Those who say it can't be done are usually interrupted by others doing it.