Dealing in specifics and avoiding generalizations
Some students have the habit of making too many generalized statements. They tend to write generalized statements in their thesis as well. In the process they tend to lose marks as nothing annoys reviewers more than too many generalized statements. It is essential to remember that a thesis is usually a focused study of something. The student is expected to deal in hard facts. He has to back every one of his statements with either a specific example, a set of statistics or a citation from a well known source.
General content can be written by anyone in the non-academic world. It does not require one to go to university or to enrol in a PhD program in order to have basic knowledge on some issue. The reason students choose to specialize in a discipline is because they wish to understand the intricacies of that particular area of study. The aim of university programs is to give the student in-depth understanding of a particular topic or subject. A PhD or a post-graduate program goes a step further and analyses a topic on a very fine level.
Too many general statements only show that the student has not fully grasped the subject or he has not done his research thoroughly. In many cases the problem is not the research. It has more to do with the writing. The student might have done his research and he would have worked hard on understanding the intricacies of the subject. However, when he puts all that information into words, he lacks the vocabulary to present them properly. If after all that hard work and all that study, a student is only going to write a dissertation in the same basic way that an outsider would then it is natural for the reviewers to deduct marks.