Concept
Social Proof
2 books in the library reach for this idea - each in its own way. When independent authors converge on one concept, it usually deserves attention.
Influence
How this book uses it: When uncertain, we look to what others are doing. "Bestseller" and "most popular" work.
The Art of Thinking Clearly
How this book uses it: "Everyone's doing it" = feels correct. Groups can be collectively wrong (financial bubbles, fashion trends). This month: identify one decision where you're following crowd - evaluate independently.