In most active volcanoes, unrest periods with dike injections are much more common than eruptions. While widely recognized, this simple observation has not been satisfactorily explained. Surface deformation in volcanoes is commonly attributed to dikes injected from shallow magma chambers that fail to reach the surface. Field observations of dike tips, many of which are blunt, indicate arrest that is primarily controlled by the local stresses in the layers through which the dikes propagate. Numerical models on the stress fields around magma chambers located in an anisotropic, heterogeneous (layered) crust indicate that, for uniform loading, a layered crust normally develops stress fields that are unfavorable for feeder-dike formation. In particular, the models, together with the field observations, indicate that an essentially homogeneous stress field along the potential pathway of a dike is a necessary condition for its reaching the surface to supply magma to a volcanic eruption.