Hail, damaging winds, tornadoes, drought, excess moisture/flooding, grasshopper infestations, pest infestations (including certain fungal spores, insects, weeds, predators, and rodents), complaining neighbors about smells & noise pollution, livestock escaping enclosures, livestock getting sick and/or dieing, reportable diseases that occur in a farmer's herd, debt, loans, no healthcare benefits, no paycheck bi-monthly or once a month only once a year, complacency around dangerous livsetock and machinery, no time for vacations or weekends-off, no bonus for salary, 99% of the time nobody will be available to help as hired labour, no such thing as an 8-hour work day, the list goes on.
Also ever-increasing regulation, lack of consumer knowledge, ever-fewer numbers of farmers (young people continue to leave the farm -- average age of a US farmer is now 57), over-production, misinformed activist groups, excessively hot or cold weather, input shortages and high prices, declining market value of crops (inflation-adjusted), and............. yes, well, the list could still go on.
Hope this helps :)