Sometimes falling asleep is like catching a bus. There's a moment when you could fall asleep, but the moment passes while you read or watch TV*, and then the moment's gone, and you have to wait for it to come around again. To ride this metaphor a little further, when the chance does come around, it might not be the express ride to morning you hoped for, but a local with a lot of stops along the way. And maybe a dog riding next to you that doesn't like to share the seat.
*Jim Gaffigan:It is amazing how much more amazing sleep is in the morning. You wake up and you're like... "I stayed up to do what?! Watch Growing Pains? What was I thinking!?"