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 deepest fears. 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 compliment-seeking behavior, 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.
So, make hard friends, and then work hard not to disappoint them.