Usually a paper is the result of months of work. These months get condensed into a document of a few pages, part of this condensation process is to replace part

Usually a paper is the result of months of work. These months get condensed into a document of a few pages, part of this condensation process is to replace part of the needed explanations with references. Unless you are one of the few experts in exactly the field the author is working on, you will have to work through these references and make the connections to the work. After this you will have to create a mapping from the clear but h are es to grasp facts of the publication to your internal representation of the topic. All of these things take time, sometimes you get to skip the part where you have to read the references by consulting a pud thesis that the paper is based on (4 pages to ca. 120 expansion), even than you have to build your internal understanding. Talking to the author will indeed speed up this process, but that essentially means having an extremely qualified privat tutor.