Labour under the delusion, illusion, misapprehension, etc. verb phrase
To wrongly think or believe something to be true
At the competition, he was still labouring under the illusion that his picture was the unique one.
Jason laboured under the misapprehension that every member of the team had respect for him.
Marry always labours under the delusion that one day she will become a superstar in the entertainment industry.
The verb "labour" should be conjugated according to its tense.