Workers' compensation is complex, even though its actual application is very straightforward: if someone gets hurt at work, they likely will receive workers' comp benefits to help them through this period of time that they are injured. This is an important element to workers' compensation. It is insurance, and most workers are covered by it. It is required by law and run by each state, though there is federal workers' comp as well.
However, there are some work accidents that don't qualify for workers' comp. For example, if the injury was self-inflicted you are unlikely to earn workers' comp. If you were off duty or doing something illegal (either by company policy, or state or federal law), this would also lead to someone being disqualified from receiving workers' comp.
Now, the actual benefits may not exactly be a massive financial boost to an injured individual -- but this insurance can still help you get by. Workers' comp can pay for medical bills, for permanent harm suffered by the individual, any retraining that is necessary as a result of the injury, and many other factors that go into a workplace accident.
A couple of other things to remember: you can sue your employer or company as a result of the injury you suffer (in addition to receiving workers' comp benefits), and your employer or company can't retaliate against you for obtaining or applying for workers' compensation. If you have any questions or are confused by the workers' comp process, you should consult an attorney.
Source: FindLaw, "Workers' Comp Benefits Explained," Accessed Oct. 8, 2014