Although his brother dropped out of college after becoming dependent on marijuana, Jonah thinks that if he starts smoking marijuana, he will be able to quit when he wants to and nothing bad will happen. This way of thinking demonstrates .

Personal Fable.

Explanation:

Personal Fable can be defined as the false beliefs of adolescents which make them believe that they are unique and thus no problem in life can affect them regardless of their behavior. This belief is formed in adolescents from the age between 11-13. The term "Personal Fable" was coined by David Elkind in his book "Egocentrism in Adolescence."

In the given case, Jonah' belief that he can quit marijuana whenever he wants to, is an example of Personal Fable. He has formed this wrong notion about himself thinking himself to be so unique that he can overcome this habit easily when no one else could. And he also believed that nothing wrong will happen to him if he will smoke marijuana.  

So, the correct answer is Personal Fable.

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