He brought up the analogy of working out: "When you're working out regularly, you don't need to force yourself because you almost have to work out; it doesn't feel right if you don't; but if you've had a lay-off and have to get back into it, it can be hard, and you do have to force yourself." This I liked much better, because it contains an important element that the first statement didn't. In this statement there is the recognition of and focus on the good that comes along with the investment of effort. And this is the key.
My yoga teacher told the class something to the effect of: "At the moment of greatest difficulty, something beautiful is waiting to be born." The idea being, I think, that it is through the difficulty that we grow into new appreciations.
I just started reading Flow: The Psychology of Optimal Experience by Mihaly Csikszentmihalyi. In it he says
we have all experienced times when, instead of being buffeted by anonymous forces, we do feel in control of our actions, masters of our own fate. On the rare occasions that it happens, we feel a sense of exhilaration, a deep sense of enjoyment that is long cherished and that becomes a landmark in memory for what life should be like....
Contrary to what we usually believe, moments like these, the best moments in our lives, are not the passive, receptive, relaxing times--although such experiences can also be enjoyable if we have worked hard to attain them. The best moments usually occur when a person's body or mind is stretched to its limits in a voluntary effort to accomplish something difficult and worthwhile. Optimal experience is thus something that we make happen....
Such experiences are not necessarily pleasant at the time they occur.
The emphasis on "make" is his. But this is the kind of forcing that is positive: when we recognize that in the reaching and in the stretching to our limits, there we are going to be the most satisfied. So yes, we need to put in effort, and to push our comfort zone, but if that effort is motivated by our sense that this is a route to feeling good.
Yes, he notes that there may be some sort of discomfort, but that discomfort is not certain--and once in "flow" easily put aside (at least in my experience).
So, if you're thinking you have to force yourself to work, remember the optimal experiences in your past. What are the moments in your memory that stand out as the most pleasurable? Are any of them flow moments? Are they memories of things that required effort? Can remembering how good those moments felt help you engage with the project at hand?