Within the framework of standard general relativity (Einstein 1915), under the assumptions of staticity, spherical symmetry and the strong energy condition, we prove that a geometric transition zone — the "reverse-bending zone" — must appear in the periphery of any finite self-gravitating system, where the t—r sectional curvature changes sign from negative to positive. This zone is bounded by the curvature zero r0, the curvature peak rpeak, and the matter boundary R; in the interval (r0, R) the sectional curvature smoothly transforms from matter-dominated spherical compression to vacuum saddle-shaped stretching. The reverse-bending zone is not a free vacuum but a forced geometry locked jointly by the interior baryonic potential well and the far-field boundary condition. Within this zone, the Misner—Sharp-type gravitational mass M(r) continues to grow: it grows faster than linearly in the region r0 → rpeak, and although the growth slows down in the region rpeak → R, it never ceases. The resulting geometric Weyl stretching together with the self-energy of the gravitational field provide an extra centripetal acceleration, which naturally manifests itself, in the weak-field approximation, as an approximately logarithmic potential and a flattening of the rotation curves. The theory yields parameter-free, falsifiable predictions that can be directly tested with existing rotation-curve and photometric data. These results show that, without introducing new particles or modifying the field equations, the forced geometry within general relativity can produce "dark-matter-like" gravitational effects on galactic scales.