be under no illusion

US /biːt əˈraʊnd ðə bʊʃ/
UK /biːt əˈraʊnd ðə bʊʃ/
"be under no illusion" picture
1.

to understand the true facts of a situation and not have false ideas

:
You should be under no illusion about the difficulty of this task.
We are under no illusion that this will be easy.