denial

from medical news today;

Although "denial" is often considered to be a form of deception, emerging research suggests that it may be due to a specific brain dysfunction similar to that observed in other neuropsychiatric illnesses.

Brookhaven's Goldstein explains the idea of impaired insight and how it might relate to drug addiction: "Patients suffering from mental illnesses such as schizophrenia often have compromised awareness of their own symptoms and the severity of their disorder. This compromise can exacerbate symptoms and reduce responsiveness to or compliance with treatment," she said. This "insight deficit" appears to originate from impairments in many of the same brain regions that underlie addiction symptoms - such as continued drug use despite catastrophic consequences, even when the drug is no longer pleasurable.

finally some concise answers about the mechanism of denial.
this research gives good insight into the addict's desire to use,
despite any consequences. often described as insanity, it is
now being viewed as a specific brain anomaly. this is a relief
to me as an explanation for the fearless attitude i displayed
when justifying my continued use.
perhaps this discovery will assist therapists in treating that
all too common symptom of denial.