Balanced difficulty curve

1. Player Achievement vs Player Advancement (Gamification Player Progression Tips)
2. Difficulty Curve vs Learning Curve (Player-Centric Gamification Tips)
3. Game Difficulty vs Challenge Difficulty (Gamification Player Progression Tips)
4. Learning Curve vs Difficulty Curve (Gamification Player Progression Tips)
5. Skill Levels vs Player Levels (Gamification Player Progression Tips)