Milestone achievements

1. Game Assets vs Game Resources (Player-Centric Gamification Tips)
2. Game Difficulty vs Challenge Difficulty (Gamification Achievement Systems Tips)
3. Game Success vs Player Success (Gamification Player Progression Tips)
4. Player Challenges vs Player Objectives (Gamification Player Progression Tips)
5. Player Expectations vs Player Satisfaction (Gamification Achievement Systems Tips)
6. Player Status vs Player Reputation (Gamification Player Progression Tips)