Generate a full detail guide on using 'gamification' to increase employee engagement. The guide should be creative and practical for HR and team leads. It must include sections on: 1. The psychology of why gamification works. 2. A detailed guide to applying game mechanics (points, badges, leaderboards) to employee training modules. 3. How to create a gamified system for sales contests or team performance goals. 4. A section on avoiding common pitfalls, like unhealthy competition. Please include a disclaimer about tailoring the system to your company culture.