A Large Step Selects a Flatter Minimum

Here is the loss f of u and v, one half of u times v minus one, squared. Its bottom is a whole valley: every point of the purple curve, u times v equals one, is a minimum.

These minima differ only in their sharpness, u squared plus v squared: steep walls near the right end of the curve, gentle ones in the middle.

The rest of the narration is in the book's Companion.