Playlist by Game Maker's Toolkit: https://www.youtube.com/playlist?list=PLc38fcMFcV_vToz9Nvc_YQTNH8hkIQ2uC

1. Valve's "Secret Weapon"

https://youtu.be/9Yomqk0C6kE

Valve's game development process:

1. Start with a goal
2. Design something - Hypothesis
3. Evaluate if design reach the goal by doing a playtest - Experiment to validate Hypothesis
4. Iterate

• Test early
• Test often (every week)
  • Player don't look up
  • Player don't learn when stressed
• Shut up and watch
  • Post game questionnaire can help as well
• Designer run playtests
• Challenge your assumptions