Human: What's the most common cause of a person having trouble sleeping? Assistant: 
The most common cause of a person having trouble sleeping is stress. Stress can come from work, relationships, or other areas of life that are causing anxiety and tension. Other causes of sleep problems include physical discomfort, such as pain or an uncomfortable mattress; medical conditions like depression or insomnia; and lifestyle factors like caffeine intake late in the day, smoking, or drinking alcohol too close to bedtime.