Craig Nakken writes in his book The Addictive Personality: Understanding the Addictive Process and Compulsive Behavior (1996) how an addictive personality may come into existence.
An addictive personality develops through a process. First, the abuser becomes dependent on the addictive process, wherein he/she searches for satisfaction. After this, the person develops a relationship to the drug and starts to build up a defense system in order to protect the drug from any kind of attack from the people in his/her environment.
Nakken describes how drug abuse is like an emotional relationship, and how the abuser tries to satisfy his/her need for intimacy through this relationship. To be dependent is not a logical state, but an emotional one. Being a relative outside this relationship we may try to understand how the logic works, but since there is no logic we will never understand, and instead we will become frustrated and disappointed. The abuser often view outsiders as objects; objects who either facilitate or threat their relationship with the drug.
If you want to know more about the addictive personality and the addictive process I strongly recommend reading the book! I found it very educating.