If one system (digesting proteins with HCl in the stomach) doesn't work, then the next system addresses the problem, if it is functioning. If the HCl is present with zinc and B1 and B6, then the proteins are digested!! DO THE PINK PEE TEST! Pat. The beet test - Heal Thyself! Eat beets.
A game designer is a person who designs gameplay, conceiving and designing the rules and structure of a game. Many designers start their career in testing departments, other roles in game development or in classroom conditions, where mistakes by others can be seen first-hand.
In some shops what they call a producer is also driving creative direction and works close with the discipline leads on creative decisions much like a game director. In other shops the game design lead is effectively the game director.