A double bind is a kind of baited trap. It is like a lobster pot or a similar type of animal trap - the trap is initially attractive and easy to get into, but then turns out to be much harder to get out of. Unlike an animal trap, a double bind works on a psychological level rather than a physical one. A double bind tricks a person into doing what the controller wants, while giving an illusion of choice.
A double bind offers some kind of benefit as its bait. With the FWBO, the bait is the promise of personal and spiritual growth. Eg.:
'Buddhism offers clear and practical guidelines as to how men and women can realise their full potential for understanding and kindness. Meditation is a direct way of working on ourselves, to bring about positive change in our lives. We teach two simple and complementary meditations. One helps us develop a calm, clear, focused mind; the other transforms our emotional life, enabling us to enjoy greater self-confidence and positivity towards others.' 
On offer are: greater understanding and kindness; mental calmness, clarity and focus; and greater self-confidence and positivity. How could anyone refuse?
Of course, a person could refuse, but then that might be taken to imply arrogance on their part. Refusal could be taken to imply that they believe they are already perfect, that they have already achieved their full potential for understanding and kindness, etc. That's already a little bit of a double bind.
However, the double bind only starts to kick in once a person takes the bait, once they start to feel that there are aspects of their lives they would like to improve, and that they might benefit from following a course of study and training, with the FWBO or any other organisation offering to teach people how to realise their full potential.
They don't need to have absolute faith in the group's teaching, only to give it some degree of credence, or at least the benefit of the doubt.
In general, groups offering to teach people how to develop their full potential, will put forward the idea that the reason why they are failing to realise their true potential, is because they are subject to certain psychological or cognitive or emotional blocks and obstacles, which they may be unaware or unconscious of. These obstacles block their energy and cause frustration and unhappiness.The group's teaching can help them to become aware of and then overcome these obstacles.
Different organisations have different ideas about the nature of the obstacles which hinder personal growth. In the FWBO, they are said to be the result of unconscious conditioning, ignorance, fear of change, etc. In a Christian based group such as the Moonies, any doubts or reservations which a student may have about the group's teaching, may be blamed on Satan putting evil thoughts into the student's mind in order to try and prevent them from reaching towards God. In Scientology, such doubts or reservations may be ascribed to the influence of 'engrams', unconscious conditionings from past lives which block the student's energy and awareness.
In a way it doesn't much matter which factors the group identifies as the reasons why a person might have failed to realise their full potential. The two key ideas are that a person has unrealised potential, and that the group's teaching can enable them to overcome any unconscious hindrances and realise that potential. These two ideas together form a potential double bind.
The double bind works in the following way: If you believe you might be failing to live up to your true potential, because of unconscious conditioning or similar factors, then what do you do about it? Do you:
(a). Give in and accept the situation?
(b). Try and break free of your conditioning?
You can of course refuse to answer the question. However, if your answer is (b), then this implies some agreement with the idea that you are 'conditioned'. To the degree that you accept that idea, to that degree you have entered into an insoluble paradox and double bind.
The paradox is: how can you attempt to break free when any or even all of your thoughts and actions may be at least partly the result of 'conditioning' (or pride, or ignorance, etc.)? If you decide on a course of action on your own account, how can you be sure that your decision isn't partly or wholly the result of your 'conditioning' (or of some other unconscious factor). How can you be sure that you are actually making a free decision, and that you haven't simply been conditioned and programmed to act in a particular way?
If a person accepts that they are conditioned to some degree, and they want to break free of their conditioning, then logically they cannot really do it by themselves, because the chances are that they will simply go round in circles, unconsciously repeating their own conditioned behaviour. They need some external help and guidance, from a teacher who has already broken through their own conditioning (to some extent at least), and who has a good understanding of the processes involved in this kind of breakthrough.
This is the whole point of setting up this kind of paradox and double bind - to make a person think they need a teacher, so that they then become dependent on the teacher. Potentially the teacher can then misuse this power, without ever being held responsible for any psychological harm their teaching may cause their students.
There is a wide variety of groups and organisations which offer teaching and guidance for people who believe that they might be failing to live up to their true potential. Some are religious or quasi-religious, offering guidance on how to grow closer to God, or to the deity of your choice. Others are more secular, offering to help people to realise their true potential, or to discover their true inner selves, or to become one with the universe.
Some of these groups and organisations may provide valuable resources; others may be cults, and it can be very difficult for an outsider to tell them apart. Many of these groups are self-regulating, which among other things means that there are no independent and objective ways to test how beneficial the group's teaching might be, the only way is to test it subjectively, by trying it out for yourself.
If, after a period of time, a person does begin to experience tangible benefits from following the practices and lifestyle advocated by the group, then all well and good. If however they experience initial benefits but then become stuck at a certain level, or if they experience no benefits at all, then at what point do they cut their losses and drop out of the training?
If they are failing to thrive, they cannot be sure where the problem lies. Does the problem lie with their own understanding and practice, or with the group and its teaching? Should they have faith and persevere, or should they drop out?
They are in a double bind because, having accepted that they might be subject to ignorance or unconscious conditioning to some degree, they can never really be sure that any doubts or reservations they may have about the group's teaching, aren't simply the product of their own unconscious conditioning. And they can never be sure that valuable insights will definitely not result from attending the next training course or residential weekend offered by the group. Or from the next course after that.
On the other hand, if they decide to drop the training and leave the group, they can never be sure that they aren't making a terrible mistake. They can never be sure in their own minds that their doubts about the quality of the teaching are reasonable and justified, nor can they prove to anyone else that their concerns are justified (because of the nature of the double bind, and because double binds work on a subjective and psychological level, and leave no objectively verifiable physical evidence to reveal their existence).
In short, they can never prove that they are right, and the group is wrong. This is one of the reasons why many religious/human potential type groups are effectively unaccountable to any outside authority for any psychological harm their teaching may cause their students.
A group only becomes a dangerous cult when it starts to abuse the teacher - student relationship and its inherent double bind. The problem with non-accountability is that, if such abuse does begin, it is likely to continue unchecked for many years, and may even become institutionalised within the group.
Using the double bind system, anyone can set themselves up as a personal growth teacher, with very little risk of ever being held responsible for any psychological damage their teaching might cause their students. Indeed, with non-accountability, low overheads, and the availability of tax-exempt religious charity status, the personal growth/spiritual fulfillment market provides an ideal business opportunity for the unscrupulous and the deluded to milk their students.