I'll start with 2 studies.
study one: They placed a rat in a tube, starved it, and put a piece of cheese in front of it. However, they clipped its tail to a device to measure the force it would exert when starving. Let's call this measure "control." Then, they introduced the scent of a cat at the back of the tube. The rat pulled harder due to the fear of the cat than from starvation. Rats exert more effort when they detect a cat's scent than when they smell food while hungry.
Study 2: "You need approximately five times more good to outweigh the bad. In our review, we have found that bad is stronger than good in a disappointingly relentless pattern." [Link to paper] Now that we have established negative emotions are stronger than other emotion, why don't you use Negative emotion for motivation?
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