There are many reasons for why a change-work session succeeds. NLP has the reputation of a “one time therapy”, which usually means that a client will only have to see you (and pay) once for resolving a specific issue.
From my experience in private practice, the one and most important factor of session success is the client’s cooperation. If the client is not cooperative, there is no use to keep the session going. If they refuse to “do” things in their imagination, as an NLP pattern dictates, you ought to make it clear to them that without their full participation it is not going to work well. In other words, you are not a magician or a therapist that is forcing his clients to get better. You could, in a way, but that would leave you exhausted, frustrated and distressed, which will lead you… into therapy yourself.

Now, full cooperation is the success secret on the surface. In the deeper realm lies a very interesting therapeutic “fact”: in many cases, as I’ve seen in my practice and noticed in more than a handful of other people’s case studies, the change the client desires starts to take place as soon as he or she becomes aware of the purpose or structure of their undesired behaviors or thought patterns. In fact, I’ve been a witness to the whole process being completed and sealed in that phase alone!
The most common example is the client who comes in suffering from severe pain, which every physician concludes to be a “phantom pain”, and before you even complete a “chunk down” exercise, the pain disappears. By facing the pain, by describing its modalities and submodalities, its subtle characteristics, and most importantly – its “message” or “intention”, it is as if that subconscious process (inducing pain to protect the core or get attention) has been “caught” and revealed, and therefore has no longer control over the nervous system’s responses to its signals. In other words, once you see how a trick is being done (what the pain was for), there’s no power to the illusion (the pain without the physiological reason).
This is a “fact” that you need to remember when you work with clients. Expect it to work, anticipate it, and you will soon notice that your work is much easier this way. Yes, you need to make your work as easy as possible, because your clients expect to get results and get them fast. NLP is a rapid change-work, not a tool you use when you’re done with listening for hundred of hours to your client’s issues.