Rousseau's spiked fence was 
    tall, ornate, intricate,
a cast-iron invitation
    to a gracious impalement.

Education must, said he,
    let the child choose 
to walk that fence,
    to learn not to walk that fence.

Skipping along its ridge
    is an ecstasy of defiance,
and tripping, a humiliation
    of pain and scars.

The child is the child's
    teacher; there are no grades,
though the dead perforce
    will fail the course.

The "Child on a fence" 
example is apocryphal 
and probably the most 
famous quote Rousseau 
never said. It is an 
extrapolation of his 
theory of childhood 
education in his book 
"Emile", arguing that 
children must be allowed 
to educate themselves. 
Only by suffering the 
consequences of doing 
something unwise will 
the child learn not to 
do it, even if the act 
of learning involves 
discomfort or pain.