TL;DR
This book touches on some of the research into what “psychological safety” is, and why it leads to higher-performing companies. In this respect, it’s similar to The Five Dysfunctions of a Team and Radical Candor: Be a Kick-Ass Boss Without Losing Your Humanity.
The main distinct Edmondson makes is between “trust” (individual, earned, based on previous behaviour) and “psychological safety” (collective, present, and not necessarily previously observed). It’s a manner of being able to overcome the initial, human response of feeling stupid or ill-informed, and speaking or asking questions regardless of who is asking and whom is being asked. It’s a challenging dynamic to overcome, but it leads to better outcomes.