How do you refrain from caring about other peoples opinions of you?

I recently asked about tips for boosting confidence. I’d like that extend that a bit further. I came across this post and it seems that a lot of how people get over their insecurities is by outside praise. To some degree, as social creatures, compliments are important, as well as a strong support system in general. But is there a point where it’s dangerous? Isn’t that kind of the basis of narcissistic tendencies (again, sounds harsh, but I’m thinking along the lines of selfies/likes)? I think that putting so much value in other peoples opinions of you can go wrong in so many different ways.
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So maybe less “how do you refrain from caring about other peoples opinions of you” and more “how do you put more value in your own perception of yourself rather than what other people think of you”
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What are other ways to build confidence outside of flattery?