This text explores the nature and legitimacy of doubt within human thought. The author distinguishes between 'false' doubts, which pertain to external objective realities and facts, and 'true' doubts. While common doubting often focuses on verifying information about the world, true doubt is characterized as an active, reflexive process of identifying errors within subjective action. This investigative doubt does not arise from simple hesitation over facts, but rather from dissatisfaction with the results of one's own activities. Through self-reflection, the thinking subject revisits previous steps to discover where a mistake occurred in the process of reasoning or decision-making. Thus, the text emphasizes the importance of critical self-reflection as the foundation for genuine understanding and the correction of unsatisfactory outcomes, shifting the focus of doubt from external objects to the internal processes of the subject.