Physical Danger
Unsurprisingly, as with the vast majority of construction jobs, stonemasons face a higher rate of injury than most professions. First, there's the obvious: cuts, bruises, and broken limbs are some of the milder injuries that occur with use (or more often, misuse) of tools and heavy machinery. Falling is possible for those jobs that require you to install rock above ground level. And dropping a twenty-ton piece of granite on your foot doesn't feel all that great either.
Then there are the less obvious dangers. Stones are heavy, especially those used in building-building. Strains in the muscles and joints are part of the gig, and unlike the occasional deep-yet-healable cutting of flesh, the aches and pains of constant manual labor build up over time. When your granddad talks about his forty years of back-breaking work, he's not speaking metaphorically―his back actually feels like it's broken.