A covalently tethered polymer molecule can spontaneously break away from the surface when polymer/surface interaction is sufficiently unfavorable. This is demonstrated in surface-initiated polymerization of a hydrophilic polymer, hyperbranched polyglycidol, from minority surface sites embedded in a hydrophobic self-assembled monolayer. As each hyperbranched polyglycidol molecule grows larger, it encounters more unfavorable interaction with the hydrophobic surface, and this leads to spontaneous bond rupture and desorption. This finding challenges the traditional view on noncovalent interaction of macromolecules with the local environment at interfaces and has broad implications for the understanding, design, synthesis, and applications of surface-tethered macromolecules.