[be] under no [illusion]

to be fully aware of the truth or reality of a situation

It is crucial to the nation's security…that we be under no illusions about reasons for this zero-loss rate.
She's under no illusion about the difficulty of the task ahead; she knows it will be a tough journey.
They are under no illusion that success will come easily; it will require hard work and dedication.
He's under no illusion about his friend's flaws but chooses to stand by their side regardless.
The team is under no illusion that winning the championship will be a cakewalk; they are prepared for fierce competition.