I've read several other answers on here, but I still don't understand. Why do both fission and fusion release energy? I know the masses drop, but then why do the masses drop on both? Fusion is taking two small nuclei, adding them together, and creating a bigger atom, why should this bigger atom have less energy? Is it because more of the mass gets stored in the strong force? Then what determines how much energy is released? The same goes for fission. A larger molecules being broke apart will approach a more stable max-energy-per-interaction form. This means that more energy should go into the bonds (I think) which would mean less mass, but still why does energy get released, and not just simply into the bonds?