Newton formulated a theory of gravity where the attraction between two objects depends on their masses and the distance between them. Normally this theory is only applied to matter, but I think it is also relevant to the way we choose between goals.
The "Gravity of Goals" equation would reformulate Newton's model like this: my "attraction" to a goal depends on the amount I value the goal (mass) and the amount of time it will take to satisfy it (distance). The longer it takes to satisfy the goal, the less likely I will pursue it. The more I value a goal, the more likely I will pursue it. Faced with multiple goals, the goal I pursue will be the one with the highest payoff (measured by subjective calculations of combined "mass" and "distance").
Imagine an asteroid hurtling through space, irresistibly pulled by a number of planets, some larger than others. That's pretty much what we are, just in a more subjective way.