After reading Stephen Levitt’s musings on whether tenure is a good thing or not in economics, I can’t resist quoting Daniel Dennett (from the incomparable Consciousness Explained, 1991, page 177:

The juvenile sea squirt wanders through the sea searching for a suitable rock or hunk of coral to cling to and make its home for life.  For this task, it has a rudimentary nervous system.  When it finds its spot and takes root, it doesn’t need its brain anymore, so it eats it!

(It’s rather like getting tenure.)

Just one perspective, of course. But useful.