I think it's flinching away from the pain of the decision to do the work - the momentary, immediate pain of (1) disengaging yourself from the (probably very small) flow of reinforcement that you're getting from reading a random unimportant Internet article, and (2) paying the energy cost for a prefrontal override to exert control of your own behavior and begin working.

The second item seems like an unnecessary hypothesis. One can simply note that stopping an activity that is currently pleasurable is difficult, if the substitute is not as pleasurable. Getting out of a comfy bed, for example, or not jumping into the swimming pool.

Either way, though, it's such an utterly trivial form of procrastination that it seems like an insult to procrastinators to call it procrastination... which leads me to suspect that your formulation is omitting some other sort of pain in the decision making process, such as an "ugh field" surrounding the subject matter.

For example, if it's painful to decide to work on MoR, it might be because it primes thoughts of people clicking their refresh buttons like conditioned pigeons, or residual feelings of obligation from previous deadline commitments. Even an extremely mild unconscious "ugh" in response to such thoughts would be likely to occur when thinking about writing, but not during the actual writing, and would be more than sufficient to keep the inertia happening... possibly even after you become aware of the existence of the inertia.

tl;dr: The twinge we flinch away from is likely an ugh field associated with meta-level thoughts about the activity, rather than a generalized pain of deciding.

(Among other reasons, the first is easily implemented by evolution as a side-effect or simple bug in an adaptive behavior, while the latter is just weird from a purely adaptive POV. We already demonstrably have "ugh fields", so adding another entity for "decision pain" seems unnecessary)