Picture this: You take a sheet of pristine A4 paper (lossless), you crumple it up to reduce size (mp3), then you attempt to uncrumple it and carefully fold it to reduce size (opus). Your sheet is still crumpled. Or, you take the pristine sheet, and just carefully fold it multiple times. In both cases it is deformed and can never be lossless again, but folded paper still has more quality, and takes less space.