yet contentment is precisely the source of happiness
然而，知足恰恰是幸福的源泉。
该句通过转折结构强调知足与幸福之间的因果关系。
"Only those who are content can experience true happiness."
"Learn contentment; true happiness lies in being satisfied with what one has."
"Happiness comes not from having much, but from wanting less."
"Only by learning contentment can one find lasting happiness."
"Happiness does not lie in abundance, but in contentment."