The first stage of change is pre-contemplation, or another way to say it is pre-thinking. This is the stage where others around the person notice the need for change, but the person doesn't see a need to change. This is where their partner says "you're eating too much ice cream," and they respond by saying "my only problem is you saying I eat too much." The person is not recognizing the problem. They don't see a need to change. They are in the pre-thinking stage.
The real challenge is how we can motivate the pre-thinker into thinking. A direct challenge isn't going to work. They aren't ready to face their problem. Instead, start by asking questions around what do they want for themselves. Where do they want to go? How is what they're doing now help or hurt progress to the goal? Help them come to the conclusion on their own (in a positive and accepting way) how their current behavior isn't helping. Getting them their is helping them into the next stage, the contemplation or thinking stage.