Quick Definition: The discipline required to seek knowledge specifically for an application of it in a stage of the pickup, rather than soaking up knowledge without a goal or the intent to apply it in field.
Brad P. explores this fallacy in the PUA Summit of 2007. Often times, newbies read too much pickup material and fail to go out in field and apply these learnings. Reading too much, at a certain point, can reach a point of no return. The newbie has gone through the material but, failing to realize the experience and principals behind opening, is unable to apply all his memorization to actual seduction and sex. The additional knowledge is simply not useful for him at this point in his game.
Intellectual Discipline is the practice of obtaining specific information to achieve a very specific purpose. For example, Neil Strauss spent 6 months seeking advice on his sticking point: getting a kiss. To this extent, he was very disciplined in seeking knowledge that helped him achieve this specific goal. If he were to read up on openers, sexual techniques, or relationship management material, he would be wasting his time.
Reading too much material is actually an act of laziness and, sometimes, fear. Many newbies and even intermediate PUAs will spend the weekend downloading e-books and videos of PUA material, avoiding the real action of going out in the field and social gatherings.
Image Source: DeviantArt