Answer:
cognitive dissonance
Step-by-step explanation:
Cognitive dissonance is the state of an individual where he or she develops conflicting beliefs, attitudes or behavior. When an individual's belief starts clashing with the new facts, they tend to resolve the contradiction to reduces their discomfort. For example, when people start to eat more junk food or adapt to an unhealthy lifestyle (behavior) and it leads to obesity( cognition), they are in a state of cognitive dissonance.
As per the question, Alan knows that drinking is harmful but still gives reason to justify it therefore he is in a state of cognitive dissonance.