Happiness Dependent on Self-Discipline?

In this post, blogger Penelope Trunk talks about the relationship between positive psychology and self-discipline. She writes (referencing a book called The How of Happiness):

The problem is that you need to find self-discipline in order to execute the strategies [to make you happy] in the first place. If all anyone needed in order to change was a scientific reason [on which happiness advice is based] then we’d all be muscular and thin.

To be sure, tucked deep inside Lyubomirsky’s book on page 274, is the admission that we need “motivation, drive and inspiration” to do the stuff that she has scientifically shown will get us to happy. But that’s the hardest part. That’s the part I need to read three hundred pages about. If we each had the self-discipline to accomplish whatever we set out to accomplish, the world would be a very different place. But what we have instead is a world divided into the people who have self-discipline (those with good careers, good bodies, and good mates) and people who don’t.

I’m not talking about the self-discipline just to get dinner on the table every night. I’m talking hard-core self-discipline, where you conduct routine investigations of how you feel and what you’re doing, and then make changes. What Lyubomirsky recommends requires a whole mind overhaul through amazing self-discipline, but I can’t even stop eating two bagels for breakfast. (Cut back just one a day! That’s like losing 1.5 pounds a week!)

I'm sure we can all identify with the struggle to maintain self-discipline, and I know that it's harder for some things than for others. (Like I can easily maintain the self-discipline to exercise, but sitting down to write fiction--for me, a writer!--is so much harder!)

I am very interested in what Trunk has to say in the bold sentence above. About self-discipline being related to "routine investigations of how you feel and what you're doing." I read that, and I thought, Yes! That's exactly right!

I sometimes think, though, that self-discipline is a psychological muscle that can be (and needs to be) exercised. So, small acts of self-discipline--like walking for 5 minutes as opposed to starting out with 30 minutes--create a mental strength that allow you to tackle increasingly daunting tasks. I wasn't always an exerciser: I used to be the ultimate bookworm and I loathed sweating. But an impromptu jog around the block one day convinced me I needed to get fit or bad things would happen.

So I started out with 5 minutes here, and over the next few years, eventually developed the self-discipline to run a marathon. Now, I will say, that since then, exercising is still part of my daily life, but I no longer have the self-discipline to run a marathon. I would have to build that back up to get there again. But the thing about having achieved something once is that I know I have it in me, which gives me the confidence to try again. (As for fiction writing... that's another post for another time.)

What about you? What role does self-discipline play in your happiness? What do you do to cultivate self-discipline?