Why do people tell you "Just hear them out?" What if I don't wanna hear it?

Stop telling us to hear someone out. I don't wanna listen! My best friend said, "Just at least hear your ex boyfriend out. He doesn't sound like a bad guy. I mean yeah he lied to you and you have the right to be pissed, but that was two years ago. Let it go already! It's not like he abused you or cheat on you. Stop holding a grudge and just at least hear him out. You don't know the real reason do you? Stop acting like a five year and start acting like a young woman. You're 18, START ACTING LIKE IT. Don't be a coward for the rest of your life."
My ex has been trying to message me and apologize. He lied and I don't wanna hear it. He only lied once but he screwed up. No!