This is not unique to writers, this desire. There are times when I need to go to the gym, but don't really feel like it. I know that if I go, and once I get cranking, I'll be fine, and I'll feel better about having gone, but what I want is to have worked out. To get the benefits without having to put out the effort …
Inertia can be a powerful thing to overcome.
That shortcut isn't real, and part of the deal is that if you don't enjoy the doing of a thing in and of itself, you are apt to not do it. If all you can see is the goal but not the trip getting there, you tend to see it as something to be endured. This tends to keep you from giving it your best, or sometimes, any efforts at all.
If you lift weights, you have to enjoy the process of picking one up and moving it and putting it down not just as a means to getting stronger or gaining more endurance, but as an end in itself; else you will find reasons to avoid it down the road.
At least that's how I view it.