How do you know when it's time to give up on someone?

My biggest weakness is I don't like to give up on people. I will hurt myself so much trying to help people because I never had anyone who was there for me and for a while it made me an extremely bitter person.

As I get older, I'm trying to learn but it's so tough for me to answer. Especially when maybe it's just a matter of me not knowing how to help the person.

How do you know when it's time to give up on someone?
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