I believe that the author is referring to the hypothesis that a frog thrown into hot water will immediately jump out again, whilst a frog placed in cold water, which is then placed on the stove and gradually heated, will sit quietly and let itself be boiled alive (i.e., we react to sudden changes, but get used to gradual ones).
Now, mind you, I haven’t boiled any frogs lately, so I can’t offer any information on how they really do behave in these situations. I only note that most people cite this story as if it were true, or at least believed.
“Kings die, and leave their crowns to their sons. Shmuel HaKatan took all the treasures in the world, and went away.”