Make the job sound much easier than it is, even if it's an easy job, in order to destroy his confidence. I'm serious. Young people in general do have a lot of unwarranted confidence about their abilities, but IT people especially need to understand they don't know everything and never will. I'm not saying be mean or condescending, but what I've done for years now is talk about the minor details of what I'm fixing and how it works, things they often don't know. Most don't say anything, but a few times a few have said they were over their heads, and one guy even quit, but the work they were doing wasn't really that complex.