It's wrong to lie to your doctor.
Carl is getting a checkup at his doctor's office, but he is embarrassed about how many sexual partners he has had.
Carl wants to get through with the checkup.
Carl tells the doctor that he has had sex with many different women of the last year.
Carl tells the doctor he is not sexually active, even though he's had sex with multiple women over the last year.
Carl's doctor screens him for STDs and finds out he is in the early stages of one, but he is easily cured of it.
The doctor doesn't screen for STDs and misses that Carl has contracted one.