Structure
Lazy Dan and I have often lamented that our most productive days ended 8 years ago when we graduated from high school. We've considered a few theories as to why we accomplished so much more back then, and I think a big part of the reason is structure.
I absolutely HAD to be at school by 7:30am, which meant I HAD to leave home by 6:45. From there I had a series of obligations until classes ended at 2:45pm, and then usually sports or activities until 5pm. Maybe a few hours to relax after the 45 minute drive home, depending on how much homework I had. In bed by 11pm, up around 6am. Repeat 5 days a week.
The contrast between that life and the life I've chosen for myself the last year couldn't be more stark. I've had no structure whatsoever, and any attempts to add some have failed or been abandoned. Maybe they've fallen short because there was no external threat of discipline: no detention for skipping class, no bad grades for incomplete assignments, no losing my scholarship if I get bad grades.
That threat of discipline eliminates options, and I guess I'm more productive when I don't feel like I have many options for how I spend my time. The mentality was "well I've got to be here, so I might as well get things done." In the absence of discipline, I have unlimited options but my #1 option is always to do NOTHING. "I don't have to be anywhere, so I don't have to get anything done!" I could try to impose some discipline on myself, but in college I quickly learned that the threat of self-discipline is an idle threat.

I'm taking care of my mother's dog this week while my parents are on vacation. Mello Yello wakes up and howls at 5:30am until someone takes her outside. She gets a bowl of food at 8am, half an apple at 12pm, and another bowl of food at 8pm. She needs to go outside every 3 hours or so until 11pm.
Mel is forcing some structure upon me. Maybe having to cut up an apple for golden retriever isn't as demanding as a calculus class, but I'll take what I can get.
Today is only the 2nd day I've had her, and here I am being (semi)productive and writing something motivational. Perhaps by the time I take her back next Saturday I'll have found a job, registered for night school, implemented a rigid workout routine, and started that screenplay I've been meaning to write.