Under no illusions phrase
Either illusions or illusion is acceptable.
My mother is worried that I will be deceived but I think I'm under no illusions about this society.
I'm under no illusions about the man I loves.
I should have been under no illusion about his real self before we got married.
Time keeps passing.
White lie
To understand easily what someone is thinking or feeling
To tell someone the truth about something that they had not understood or received false information
"Under no illusions" is supposed to derive from either the medical or legal parlance.
It is impossible for a person to change his or her innate or fundamental nature.
He said he would quit alcohol, but he still can't desist from drinking. Once an alcoholic, always an alcoholic.