Stereoelectroencephalography (SEEG) is a powerful technique for delineating the epileptogenic zone network in patients with drug-resistant epilepsy, providing direct access to both superficial and deep brain structures. However, its clinical value depends critically on the accurate interpretation of the recorded signals-which requires clear understanding of what we are actually recording, and what we are not. In this review, we examine the fundamental biophysical principles underlying SEEG signal generation, mainly the anatomical organization of brain structures and their distance from SEEG contacts. We address the types of epileptic patterns that SEEG can detect and how their interpretation depends on the referencing montage. Building on these concepts, we discuss the types of activity that may be missed or misrepresented. Finally, we explore emerging strategies to extend the field of view of SEEG electrodes. This review is intended both as an introduction for newcomers to the origin of SEEG signals and as an update for experienced users, reaffirming key concepts and presenting new methodological perspectives.