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.
1. Doing something extremely well
2. Behaving in an extreme or remarkable manner
1. Holly was in rare form during her speech, so she got the first prize in the competition last night.
2. Corrine: I'm going to buy Christmas presents for everybody. Do you want to go with me?
Laura: Oh...My kids are in rare form today, so I cannot go with you. Sorry!