When Is It Time to Walk Away from a Conversation?

Questions about how to discern when it’s time to walk away from a conversation, and how to cope with people charging you with being prideful and legalistic when you’re doing your best to be humble, fair, and gentle while sharing the gospel and defending the faith.  

• How do you discern when it’s time to walk away from a conversation? If the person is hard-hearted, is it worth it to keep trying to sow seeds? When does it become “throwing pearls before swine”?
• I do my best to be humble, fair, and gentle when I share the gospel and defend the faith, but I’m still frequently accused of being prideful and legalistic, which is painful because I actually care very much about people’s souls. How do you cope with this when you have similar experiences?