Reading a Lustiges Taschenbuch (Der Fluch der Hexe, Vol. 538, pg. 12) I came across an episode where the three nephews and Onkel Dagobert are miniaturized due to magic and encounter a spider. The following conversation occurs:
Nephew: Spinnen sind harmlos, das lernt man jedenfalls in der Schule.
Onkel Dagobert: Und dann belehrt einen das Leben eines Besseren!
“And then life teaches you better” seems to be the sense of Onkel Dagobert’s statement, but I am not sure how to interpret eines Besseren. My guess is that it a contraction of “eines besseren Fakts” (in the genitive + nominalization of besser) -> of a better fact.