People follow crowds, show them the crowd

"Join 50,000 marketers who read this newsletter." You've seen this pattern everywhere because it works everywhere. People use the behavior of others as a shortcut for their own decisions.

The number needs to be specific. "Thousands of users" is vague and feels made up. "12,847 teams use this" is specific and feels counted. Specificity implies precision, and precision implies truth.

The group needs to be relevant. "50,000 people" means nothing. "50,000 ecommerce managers" means "people like me already decided this is worth it." The closer the described group is to the reader's identity, the stronger the effect.

Timing matters too. Show crowd proof at the point of decision, not at the top of the page. A visitor at the top of the page is still figuring out what the product does. A visitor near the sign-up form has already figured that out and is looking for validation. That's when "Join 50,000..." does its work.