know one's own mindto be very sure of what one's opinions are and what you want to do
[TahlilGaran] Dictionary of Contemporary English ▲
know one's own mind v. phr. To no( hesitate or vacillate; be definite in one's ideas or plans.
It is impossible to do business with Fred, because he doesn't know his own mind. [TahlilGaran] English Idioms Dictionary ▲