The more difficult the victory, the greater the happiness in winning.
The study of psychology is the study of life's solutions.
解释:齐国是强国,利用它的强大进攻宋国,让他逞强,燕国就可以乘机打败齐国;齐国是大国,利用它的大国野心吞并宋国,增加土地,燕国就可以乘机进攻。
Sustainability isn't an option—it's a necessity for the future of our planet.