is a quote from the Enzensberger interview in ZEIT Magazin Nr. 33 (12.8.2010).
Teaching students means even teaching yourself -as thoughts are being built during speaking.
The quote seems to go back to Kleist “Über die allmähliche Verfertigung der Gedanken beim Reden” who recommended discussing difficult problems with colleagues. Unfortunately scientific congresses like the one that I attended recently include only some pseudo discussions at the end of talks – cut and dried opinions of self important persons.