People often feel more altruistic when they have helped without receiving payment or implied social pressure than when offered a reward for doing so.This is best explained by:

Question

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The overjustification effect is the tendency for intrinsic motivation to diminish for activities that have become associated with extrinsic rewards. In this case, the offer of a reward may cause the person to view their action as less altruistic and more motivated by the reward, leading to a decrease in their intrinsic motivation and subsequent feelings of altruism.

People Often Feel More Altruistic When They Have Helped Without