A surprising amount of people don't know the causes of insomnia. They just have difficulty sleeping, but have no way of solving it. It's something I don't enjoy hearing, but I've experienced it. I've been in bed, tossing and turning, hoping I'd fall asleep. It's frustrating and I don't think anyone should have to go through it.
The first cause is stimulation and there are many forms of this. The obvious ones revolve around caffeine. Coffee, soda and other things that cause a real problem with your sleeping. It's also important to note that stimulation can take on another form. Using your computer before you goto bed will actually keep you up. It keeps your mind stimulated and makes it hard to fall asleep.
Another one of the causes of insomnia is inconsistency of sleep patterns. I'm sure you've heard that our body has our own biological clock. Well, that clock wakes us up, but also puts us to bed. When we start to disrupt this clock, it's hard to sleep. I had a night shift job and that really made things hard for sleeping because I worked 10 hrs a day, so I got three days off in a row. My sleeping patterns would change up on my 3 days off and it made it extremely hard to sleep.
Stress and anxiety is another big reason that could be causing the problem. Never before have we lived in a society where people are stressed out and full of anxiety. The reason that these can cause problems is that they make us worry. Worrying is really the concept of your mind constantly analyzing. You can't sleep when your mind is in a worried state of analyzing.
One of the big causes of insomnia is a very inactive lifestyle. Our body is designed to be worked. Sitting at your desk all day and than moving to the couch in the evening, isn't exactly what a typical human was designed to do. We were expected to do a lot of work.