This is a particularly difficult Rule for most people to implement and practice. Especially so if you've been using Job Fairy techniques heavily for years, as most of us had been. Full disclosure is never a good idea; the less people knew about our backgrounds or thoughts or skills, often the better off we were. However, since Job Fairy techniques are all about self-defense, not offense, this Rule can be observed and made to work for you. It's really not as much of a limitation as you might think.
Firstly, none of us Fairies ever does things like claim a degree that we don't have. It's just too easy to catch someone telling a whopper like that. In addition, we also don't think it's a good idea to claim skills that you don't have. If you've used Unix, sure, put it down as a skill on your resume. That's valid. However, don't claim you were a Unix system administrator when all you've ever done with it was route all your backups to /dev/null. You'll be caught, and it won't be pretty when you finally are.
There are other aspects to this Rule. Job Fairy techniques, once learned well, can be quite powerful. They're not to be used in order to screw people over. They're for self-defense; using them to take advantage of others is a bad idea and creates unhealthy karma. Many of us Fairies have been in situations where we could have used our Fairy skills in order to get an edge over others; instead, we chose not to. In most of these cases, we were laid off, and the other person remained. Crazy? No. With our superior job-hunting skills, we landed on our feet, pocketing healthy severance packages while starting new and better jobs swiftly. More money, less heartburn. It's the only way to live. When you run into a bad job situation, you don't stay. You'll only open yourself up to stress-related disorders like cancer or depression. When a snake gets too big for its skin, it sheds it and moves on. Sure, there's a period of discomfort, but then it's over and the new skin looks lovely.
Secondly, I have always thought people give too much of themselves away too soon. Women, in particular, open up too fast - trying to connect with people all the sooner. It doesn't work. People tend to judge you quickly; the sooner they have information about you without really knowing you first, the sooner they'll look down upon you. Especially if you have skills that might be construed as superior to theirs. Assume that people are all very insecure, and they'd be willing to believe the worst of you so that they could feel better. Even when it's not a bad employment climate, frequently, people still feel that their jobs are threatened.
Your job is to reveal as little as possible until these people like you as a person. At that point, you will figure out that either you fit into the corporate culture, or you don't. If you don't, keep looking for another job. Job success is all about fitting in, not actual skills. I can't tell you how many times I've been sent in as a contractor to fill someone's place - a someone who was far more skilled than I was. Nevertheless, my soft skills were what got me the job every time.
Suppose that you do fit into the corporate culture. You still don't reveal anything unless it's absolutely necessary. Less is more. No one is entitled to the details of your life. Most people can be deflected by merely changing the subject - especially to a topic on which they'd love to hold forth. Ask them about their widget collection, their children, their pets, or their house. Ask them open-ended questions about the project and the people involved. I've never met anyone yet who could resist the temptation to blather about the politics of a particular project they're on.
If you play it close to the vest all the time, people will assume you're more powerful than you are, more popular than you are, and that you have it more together than you do. This is definitely an impression you want to create. As we've said before, controlling the variables is key. Make sure they see only the side of you that you want them to. The less information they have about you, the better.