to rack one's brains; to think of every possible way to do something, often used in a negative sense to describe scheming or using calculated effort

to set one's heart on something; to be completely focused or concentrated on one thing

the central idea, gist, or fundamental theme of a text, speech, or system of thought

to waste one's energy or thoughts on a futile effort; to scheme or worry for nothing

To think through carefully; to invest mental effort into considering something thoroughly.

to rack one's brains; to take great pains to think something through or find a way to do something