What generally causes hard stools?

Slow transit time: Slow passage of stool allows the colon to pull out water (it's like a 3rd kidney). Low intake of fiber, fluids, inactivity, meds e.g. Narcotics, underactive thyroid, elevated blood calcium level, depression, other factors all can play a role.

Inadequate fiber: Increase your fiber and water in your diet. Most people have symptoms of constipation, infrequent bowel movements, anal fissures, hemorrhoids, diverticulitis and several other problems.