Marijuana has a calming effect on most people, and this is what prompts them to keep using it. If a person is dealing with intense stress or anger, smoking marijuana often can help to regulate the individual's mood--but this habit can turn into an addiction. And for some people, marijuana can lead to other health problems, and since it can be hard to stop smoking the herb for some individuals, this poses a serious issue.
Yes. Addiction is also state of mind (as well as sometimes chemicals inside substances that makes them so). A person can lean toward any habit that makes them feel good. Many will argue that Marijuana is something that they can "take or leave" and that they don't "have" to have it to feel good- but the point isn't weather you can take or leave it. It's how a person feels that draws them to something that makes them feel good (or in some states now, less pain - legally) and whether they want to experience that feeling over and over again. Which is a form of addiction. It's not just about the drug itself, it's about the state of mind and the realization that "something" can make you feel better. Psychologically, it doesn't have to be a drug that people turn to - but Marijuana is just as addictive to some as the escapism that video games provide to the players who play them.
Yes, you can get addicted to marijuana, you can be addicted to any drug. You can end up not only wanting but craving a high that requires you to have this drug. It becomes a habit that is very hard to break and that is why people continue to smoke it.
According to the Casa Palmera, a recovery organization, regular use of marijuana can cause addiction to the drug. My personal opinion is that even someone who regularly uses marijuana for a couple of years can still break the habit without any addictive behaviors like withdrawal. I tend to think of marijuana as a habit like eating chocolate regularly, not much of an addiction except in some extreme cases. I don't feel that marijuana is nearly as addictive as other things like cigarettes or cocaine, but I can agree that it's probably addictive to some who do use more than once daily for a very long time.