Why do I never go to bed when I intend?

Almost every night I tell myself, “I should go to bed at X time so that I’ll be able to wake up in the morning with a minimal amount of pain.” Almost every night, I stay up way past when I mean to go to bed, usually doing nothing particularly useful. Almost every morning, waking up is an incredibly painful affair because I have cut my sleep woefully short by my negligence.

Is there something going on psychologically that I need to address? Or am I just an idiot?

I have a somewhat dubious relationship with my alarm clock. Sometimes I don’t even hear it, even though it’s plenty loud. But I still wake up for stuff—just not with as much time as I had wanted. And not as gently as I always hope.