The influence of nuclear spin on the magnetic hysteresis of a single‐molecule is evidenced. Isotopically enriched DyIII complexes are synthesized and an isotopic dependence of their magnetic relaxation is observed. This approach is coupled with tuning of the molecular environment through dilution in an amorphous or an isomorphous diamagnetic matrix. The combination of these approaches leads to a dramatic enhancement of the magnetic memory of the molecule. This general recipe can be efficient for rational optimization of single‐molecule magnets (SMMs), and provides an important step for their integration into molecule‐based devices. DIY magnetism: The quantum tunneling in a mononuclear Dy‐based complex, which already behaves as a single‐molecule magnet (SMM), can be drastically reduced, improving the capability of the molecule to store magnetic information. This improvement is brought about by using isotopes of DyIII without a nuclear magnetic moment, thus suppressing the hyperfine interaction, and by dilution of the SMM in a diamagnetic matrix, thus cancelling the internal field.