Social proof is the concept that people observe others' actions to guide their own behavior in a given situation. Essentially, if many people are doing something, we tend to feel we should do it too. This tendency is strongest when we’re uncertain about what to do and assume others might have better knowledge. Often referred to as "herd mentality," social proof leads us to trust choices that are popular or widely accepted. This is why we seek advice, assume busy restaurants are good, and why businesses highlight customer reviews and testimonials. In digital marketing, it means people are more likely to read, share, or engage with content if they see others doing it first.