to contrast the misery of the past (often specifically the pre-1949 "old society") with the happiness of the present; to reflect on past sufferings so as to better appreciate the hard-won happiness of life in the new society

(idiom) to think deeply and hard; to rack one's brains to find a solution. Also written as [[冥思苦想|冥思苦想|ming2 si1 ku3 xiang3]].

to rack one's brains; to think hard