If you are reading these lines it is because the same people you just read in the prologue have convinced me. Although I have been thinking about writing this book for seven years, the experience in its application made me back out. Although the method is simple and elegant and extremely easy for a normal person, what is not normal is to find "normal" people. I found that a paradox in the form of a curse inevitably appeared: while those who took it as a simple playful activity succeeded without further ado, those who really cared had all kinds of difficulties. 
So, once the method was protocolized, I focused on finding out what was happening on the people's side and I found, among others, after-effects derived from incorrect concentration exercises to which they were subjected for years and which are not at all harmless, they are severe and difficult to treat. I also found pharmacological treatments, as well as various addictions, dietary deficiencies and traumas of all kinds that interfered with the process. 
The problem was that these obstacles, instead of becoming more limited, became more varied as I studied more people, but each person is a world and became unapproachable. 
In these years I limited myself to apply it individually, monitoring each person until they do them, fix them, learn to do them and can repeat them without further problem, which takes little time, but the inconvenience is having to come all the way here. 
So when they asked me to write this book they convinced me by saying that there would be people "with little dust in their eyes", a quote that resonated with me, and that they would support with their testimony. For my part, I have described with the utmost precision the method so that by following it literally there are no inconveniences in achieving it. In addition, I relate the most frequent obstacles I have encountered, so that the reader can keep them in mind and identify them if that is the case. 
The jhānas are the gates of enlightenment and it is not a matter of keeping the door hidden any longer because there are people incapable of using a simple key that opens them. The method is so powerful and elegant, I can't resist considering that it is intrinsically linked to human nature itself and that in other times, remote times perhaps, the social networks of that time connected devas and humans. 
If you are one of those with little dust in your eyes and you care, take it easy, read it slowly several times and do it. Stepping out of the world and contemplating it will change your life, as it did for Buddha himself.