John is a 45 year old accountant who owns his own business. …

John is a 45 year old accountant who owns his own business.  He is rather shy, but needs to entertain for business frequently.  He noticed that when he drank several beers, he was able to socialize better during the business dinners. Lately, he has started drinking whiskey instead of beer and finds that he needs to drink more than he used to so that he feels comfortable socializing. This is an example of: