How does hinduism reinforce followers' willingness to remain within their castes?

The reason is Hinduism, follow the Caste system in which its is clearly mention about the Varna system in which four major section were divide and people who born under particular classes have to remain under it till his/her death.

Explanation:

India's caste is perhaps the world's greatest lasting social authority. caste incorporates the complicated ordering of social clubs based on religious purity and defined by birth.

They have certain caste laws which reinforce followers willingness to remain within their castes these laws are such as:

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sense of self-interest