This is just a short post.
The Challenge is different for each person and depends on the hidden fear that the person has not come to face yet. In a nut shell the challenge is another person giving you an easy way out or lets you give in to your instant gratification satisfaction.
In a drug and alcohol rehab this could be smuggled in drugs or alcohol. At work it could be a tip or pay off to do something that is against your code of conduct. at school or university it could be cheating at a test or essay.
At this point you will be challenged and your response to this challenge could mean that you start over or get punished in some way. The first time may not be too detrimental but this challenge can be repeated when you return from your quest and then it is real and can be really detrimental.
To illustrate this. A client enters Rehab and smuggles in some cannabis. After some time he learns the pattern of the staff and asks another client to have a smoke with him. Both clients have a smoke and they get discovered. they both get kicked out of rehab, but are told that they are more than welcome to come back in 2 weeks and start over, however they must go through the assessment again and start from scratch. If all works well they do come back, and welcomed back. But, this time they are put on a behavioural contract that binds them to strict adherence or they must leave.