Answer:
Sink-Cost Fallacy
Explanation:
According to my research on studies conducted by various behaviorists, I can say that based on the information provided within the question the mental bias that describes Les's behavior is called the Sink-Cost Fallacy. This fallacy/bias refers to when an individual relentlessly continues's a behavior solely because of the resources that they have invested, either being time, money, or effort. Which in this case since, Les invested money into the drink so he does not want to waste it even though it might make him sick.
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