Some people don't have the willpower to quit anything.

And I've seen plenty of people who would benefit greatly from laying off the pot for a while who simply give excuses like "You can't get addicted to pot" or "at least it's not <insert other drug here>".

The fact is weed isn't for everybody, and some people do get some form of addiction or another. It's a matter of the affects it may be having on your life and if that's something you want to change.