Many time authors use well-known proverbs to express their ideas. Proverbs are short sayings in common use that very aptly express some obvious truth or familiar experience.
To understand proverbs, you must be able to read between the lines. You cannot read the proverb " A rat that has but one hole is soon caught" is not really concerned with the fate of rats. What it implies is that anyone who relies on just one thing will fail.