Fulfillling a promise is but one act of volition. It exemplifies volition, but it doesn't characterize volition.
Volition or will, for a person, is essential self-determination of events. 'Self' is the idea that, with this mind, this conglomeration of sensory inputs, ideas, interpretations, predictions, designs, imaginings, feelings, and opinions that compose a unique world-view, there is a core something, a driver of the body-vehicle, a puppetmaster pulling strings, a ghost in the machine, something greater than the sum, and that whether it survive death or not, like a cup that has the capacity to be filled, it has capacity to 'bring about.' It brings about ideas, it brings about events: the instigation of relation, the stubbornness of belief, the perfection of mathematics, the timeliness of birth, the nobility of leadership, the propriety of care, the rule of law, the decomposition of truth, the safety of institution, the solidity of companionship, and the fluidity of culture. For all that mankind has done, he owns up to every bit of it. He owns it. Without owning it, there is no essence.