Which excerpt from "the enigma machine” supports the idea that allied forces expected the germans to complicate their coding system?

The excerpt from "The Enigma Machine” that supports the idea that Allied forces expected the Germans to complicate their coding system is the following: 

"The Germans knew their enemies were listening to their secret radio communications, but they were confident their messages were undecipherable.

The ENIGMA machine so enciphered the messages that the Germans assumed the contents could be deciphered only by duplicate ENIGMA's set according to precise and frequently changed settings."

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i think that will have something to do with the mississippi river but google will know the full answer for sure

onto a large boat, and mark the water level that the boat sinks to. then, take the elephant out and put a bunch of marked weights onto the boat until it reaches the same water level. add up the masses of the weights to get the weight of the elephant.