The paper hypothesizes that human comprehension is limited because only those human traits and abilities emerged in the course of evolution which are important for the preservation of the species. For this reason, man can probably become aware of only a part of the entire reality. We are probably forever prevented from intuitively understanding the intrinsic nature of spacetime. Our notions about space and time developed and evolved in an environment where the maximum speeds consciously experienced are far smaller than that of light. As a consequence, the notions of Newtonian mechanics, of which the concept of inertial frames of reference is a part, attained the status of intuitively self-evident laws of nature. With the development of general relativity a (counterintuitive) insight emerged, viz. that gravitation is only a manifestation of the fact that particles in spacetime describe geodesics, and that the geometry of spacetime, described by the line element, is determined by the distribution of mass and energy in space or alternatively, that masses are a manifestation of the curvature of spacetime. This effectively obviates gravitational force. The only space accessible to immediate intuition is fiat Euclidean space, where the geodesics are straight lines---arguably of privileged shape. There, inertial reference frames which can be realized in practice by a number of different and mutually independent procedures, are also mathematically privileged because in them, the coordinates of (mass) points moving freely (i.e., under the influence of no force) are linear functions of time. Gravitational force appears there as something extraneous that keeps the points from moving uniformly on the geodesics of flat space, i.e., on straight lines. In the curved spacetime of general relativity, the geodesics may have any shape, are thus no longer privileged and for this reason general relativity, in contrast to Newtonian mechanics and special relativity, no longer produces any privileged frames of reference.