2. Because a great friend genuinely cares about you, they know when and how to be honest.
My husband often repeats something he heard from his late father, that when you love someone, you're honest with them even if it hurts. You tell them when they're doing something wrong because you care. This goes for family and friends.
I'm not talking about when your friend asks you if she thinks she looks fat in her dress. That may just be a cry for love, asking you to help tame their inner-critic. We all need coaxing sometimes. What I'm talking about is when they're doing something you know could ultimately hurt them and they continue going down that path. When I was 25 I dated someone none of my friends liked, and my one girlfriend was finally brutally honest to me about it. I couldn't see through my own point of view at the time and had to learn my own lessons. But what my friend said stuck with me until I finally had the courage to let him go.