For most people who have sleeping troubles, which of the following is the most usual cause?

M: Joining us now is Dr. Joanne Getsy, medical director of the Drexel Sleep Center. Dr. Getsy, welcome!
W: Good morning!
M: Good to have you here. We talk about insomnious people who can’t seem to get to sleep. Then you have folks, I think,  [1]I’m one of them who just don’t sleep because you’re just too busy. I meant to go to bed at nine last night. It was 22: 30 before I climbed into bed. So how do you separate the two?
W: [1]Oh, I think most people who complain of trouble sleeping are really in your category. And there is just the 24-hour world. We have too much to do. And there is just not enough time for sleep. And I think the important thing is that people don’t understand the importance of sleep. You know, we exercise and we eat right and we try to do what is right for us. But we forget that sleep is as important as all of those things.
M: It is not a luxury. It’s a health thing. The National Institute of Health says 10-15% of the general population struggles with chronic insomnia. And some of those people do fall in the category of, they can’t sleep, as much as they try, they can’t.
W: That’s right!  And when we see them at sleep specialists, We can usually determine from what they tell us, whether they really have insomnia and have trouble sleeping, or whether they just can’t seem to find the time for sleep.
M: Alright. Primary insomnia, again, these are people who can’t sleep enough because of the health condition. But they simply can’t get to sleep. You have got some advice for them, including "To stay asleep, you must stay awake. "
W: Yes!  [2]Well, the important thing is to keep a schedule. People that have trouble sleeping really need to schedule when their sleep is going to be. They must try to find the time when they’re going to be asleep and the time they must stay awake.
M: Even, even in fact I’m not tired until 3 a. m. ?
W: Then, then you go to bed at 3 a. m.
M: Go to bed at 3 a. m. ? And then get up and go to work at 7 or 8. . .
W: Exactly! [5]And we actually make a schedule and that means there’s no point in lying in bed for two hours. Your mind wants to see production.
M: Do you say "Set a bedtime" and "Don’t lie awake in bed"?
W: Absolutely right!
M: And also "Persevere".
W: Well, it’s hard, you know.
M: So, this isn’t gonna be an overnight change.
W: Trying to learn to sleep is a long process and it takes a lot of dedication. You have to stick with it. And don’t give up.
M: And so this is someone who’s gonna really stick with the program.
W: Precisely. It’s like quitting smoking or drinking. You have to really put the time in it. If people are ready, it would work. But it is not easy.
M: Let’s talk about something you call "sleep hygiene—the tips you say anyone can use to improve their habits. "Make sleep a priority". And then let’s get back to people like me. Right?
W: Well, that’s hard. I mean we have so many responsibilities in the world. But if you find that your sleeplessness is disturbing the way you feel during the day, then you have to make it a priority.
M: And then "Make your bedroom comfortable".
W: Well, I mean your bedroom needs to be comfy and cozy. You shouldn’t have your computer in your bedroom, and you shouldn’t be paying your bills while you are lying in bed. It ought to be comfortable and inviting.
M: We all know that caffeine will keep us awake. But you say "Don’t have caffeine after lunch". Someone going to bed at nine or ten, I mean does it really stay with them that long?
W: [3]Caffeine can stay with you up to 10 hours. And so you have to make  sure you stop if it’s
bothering you and if you have trouble sleeping, you shouldn’t have caffeine after lunchtime.
M: I’m reading the next tip. I hate to tell you that in about an hour I am gonna be taking a nap, but you say "Don’t take a nap during the day".
W: Well, I think naps are good. If they are people like you, you have a crazy schedule and you can’t get to sleep and maybe tonight you have something else that you have to do. And I think in that type of situation, a nap is good. It’s gonna revive you.
M: Do you like a twenty-minute nap or two-hour nap? I mean is too much bad?
W: [4]Too much is too bad. You have to keep it less than 45 minutes. Because if you take a nap that’s longer than that, you will end up getting deep sleep then you wake up feeling worse instead of better.
M: Alright. Dr. Getsy, it’s good to have you here.