Stimulus — a sharp stick, with which the ancient Romans drove cattle. In psychology, the influence of an external factor that causes direct coercion to act (to run away from … or run to …). Often, incentives are called incidental circumstances that spur on towards the main content of the activity. “And then there’s…” (the sun bakes, they give you money, you want to write…) Incentives influence the choice to a small extent, more often they affect the speed of movement.
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Motive is the reason or cause for action for which a person does something. That which determines the choice (argument in favor of this or that choice), explains the behavior of a person, gives it meaning.