Stereotypes and beliefs are made from some thinkings thoughts without rational basis or reason. If we think some an object or other people has have some  an image or characteristics without any reason, it can make  the stereotypes or beliefs

By the way, it seems that there are some differences between them. In general, stereotypes are the negative thinking thoughts about some objects or people. Aswhile Meanwhile, beliefs are the positive thinking thoughts. The first leads to the discrimination or disencouragement, but the latter can make motivation or encouragement.

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-The noun for think is thought

-Be careful of overusing "some". Most often "a" is suitable enough. The sentence isn't wrong with "some", but "a" is more natural and, in fact, easier

-I think beliefs are generally more based on facts or evidence. Stereotypes are based off judgements, but beliefs come around due to some evidence. For example, children beliee in Santa Clause because they see presents from him and read stories about him and see movies about him. Likewise, my mother believes she's an expert at microsoft because she learned how to copy and paste haha Great piece again and way to be timely with it!