If you had a job that involved lifting heavy objects, there would likely be legal guidelines for your employer to follow to ensure your safety. These guidelines might address your work environment, the load you can carry, and the pace of your work, including mandatory breaks. But if your job involves heavy mental loads, the rules aren’t so clear. Since the brain doesn’t perspire, ache, or give obvious signs of strain, we often assume it never really tires — or that its fatigue can be ignored to meet a deadline or finish a 2 AM call.