tl;dr: If you struggle with motivational problems, it's likely that the problem is not intrinsic to you, but instead that you haven't yet found work that you find very interesting.  

How I discovered how to do great work

Last winter I did something that I had never done before. I spent ~1500 hours working on genuinely original scientific research.

I had done research for my PhD in pure math, but faced squarely, the problems that I worked on were of very little interest to anyone outside of the fields, and I was not very engaged with my research. Pure math is very heavily stacked with talent, and the low hanging fruit has been plucked, so unless you're one of the most talented people in the world, your prospects for doing anything other than derivative work are very poor. 

What I did last fall was entirely different. As I trained to be a data scientist, I found that there's far more low hanging fruit in the field than there is in pure math, and found myself working on novel problems that are of broad interest almost immediately.

Having very high intrinsic motivation made a huge difference. I found myself spending all waking hours (~90 hours / week) working on it obsessively, almost involuntarily. Once I emerged, I realized that what I had done over the past ~3.5 months was far more significant than all of the other work that I had done over the span of my entire life combined. I was astonished to find myself having ascended to the pantheon of those who have made major contributions to human knowledge, something that I hadn't imagined possible in my wildest dreams.

The problem isn't "laziness"

Many of the most interesting people who I know are achieving at a level far below their potential. They often have major procrastination problems, and believe this to correspond to them having a character flaw of "laziness". I've become convinced that these people's problems don't come from them being insufficiently disciplined.

Their problems come from them spending their time trying to do work that they find boring. If you find your work boring, it's very likely that you should be doing something else.

References

My position is not unique to me: it's common to extremely high functioning people.

[1] Steve Jobs created Apple, which owns ~0.1%+ of the world's wealth. In his 2005 Stanford commencement address he said:

I'm convinced that the only thing that kept me going was that I loved what I did. You've got to find what you love. And that is as true for your work as it is for your lovers. Your work is going to fill a large part of your life, and the only way to be truly satisfied is to do what you believe is great work. And the only way to do great work is to love what you do. If you haven't found it yet, keep looking. Don't settle. As with all matters of the heart, you'll know when you find it. And, like any great relationship, it just gets better and better as the years roll on. So keep looking until you find it. Don't settle. 

[2] Bill Thurston is one of the greatest mathematicians of the 20th century. He formulated the geometrization conjecture, which subsumes the 100 year old Poincare conjecture, considered one of the ~7 most important unsolved problems. He describes his own character as follows:

My attention is more inward than that of most people: it can be resistant to being captured and directed externally. Exercises like these mathematics lessons were excruciatingly boring and painful (whether or not I had "mastered the material"). I used to think my wandering attention and difficulty in completing assignments was a defect, but now I realize my "laziness" is a feature, not a bug. Human society wouldn't function well if everyone were like me, but society is better with everyone not being alike.

[3] Scott Alexander / Yvain is widely regarded as a great writer. Political celebrity Ezra Klein characterized his blog as fantastic. Scott wrote:

On the other hand, I know people who want to get good at writing, and make a mighty resolution to write two hundred words a day every day, and then after the first week they find it’s too annoying and give up. These people think I’m amazing, and why shouldn’t they? I’ve written a few hundred to a few thousand words pretty much every day for the past ten years.

But as I’ve said before, this has taken exactly zero willpower. It’s more that I can’t stop even if I want to. Part of that is probably that when I write, I feel really good about having expressed exactly what it was I meant to say. Lots of people read it, they comment, they praise me, I feel good, I’m encouraged to keep writing, and it’s exactly the same virtuous cycle as my brother got from his piano practice.

[4] Paul Graham is the co-founder of Y-Combinator, a seed funder with a portfolio of combined value exceeding $30 billion (with investees including Dropbox, AirBnB and Stripe). In What You'll Wish You Had Known he wrote

One of the most dangerous illusions you get from school is the idea that doing great things requires a lot of discipline. Most subjects are taught in such a boring way that it's only by discipline that you can flog yourself through them.

Now I know a number of people who do great work, and it's the same with all of them. They have little discipline. They're all terrible procrastinators and find it almost impossible to make themselves do anything they're not interested in. One still hasn't sent out his half of the thank-you notes from his wedding, four years ago. Another has 26,000 emails in her inbox.

I'm not saying you can get away with zero self-discipline. You probably need about the amount you need to go running. [...] But once they get started, interest takes over, and discipline is no longer necessary.

Do you think Shakespeare was gritting his teeth and diligently trying to write Great Literature? Of course not. He was having fun. That's why he's so good.