I think it is endemic to be over-committed in our society. There are so many things to do; so many opportunities; so many responsibilities.
It's important to make choices and good choices in how we meet our conflicting commitments.
I'm a bit over-committed tonight, but spending a few minutes to write in this blog is sufficiently important to me that I chose to spend the time, even though it made me late for other things.
When we have multiple commitments, we have to choose which to honor. It's easy to let the commitment to a long-term writing project slide--there's always tomorrow in which to work on it. But if you don't make the choice to fit in the time for the dissertation, it doesn't get done.
That makes it important to have a good relationship with your work, so that you don't feel bad fitting in fifteen minutes of work here or there. It's the regular choice to work on the project that gets it done. With regular work, we get used to working on the project. If that regular work is done in a way that helps develop a positive relationship with your work, then you'll gain momentum; the work will become easier and the amount accomplished will grow.
When you're over-committed, the choice usually isn't mutually exclusive; while I don't advocate being late for appointments, one can choose to make the time for the writing at the expense of some other commitment. And that habit of choosing your work--even a little--is the habit that will get the project done.