because they creates the norms of what is expected, in the specific context of that team. 

because If people feel safe, they can take risks with raising ideas or concerns.

because when people feel safe, they can focus on the problem rather than focusing on surviving the meeting or the entire project

because they create psychological safety which can be defined as “being able to show and employ one’s self without fear of negative consequences of self-image, status or career” 

because they set ground rules on what is acceptable or expected behaviour, making it safe for everyone to participate.