Hard friends will help you to succeed; they won't let you slack off or distract you, and they may shame you for procrastinating or shine a light on your insecurities. They're constantly trying to remind you that your dreams matter and how even a momentary lapse in concentration can quickly spiral out of hand.
Hard friends won't humor your depression; they won't put up with your compliment-seeking, self-pity or narcissism. They don't care about your feelings because they don't want you to feel good, they'd rather watch you succeed.