Dale Carnegie's book has sold over thirty million copies, and nearly a century later it still sells more than a quarter-million copies each year.

He encourages people to listen, be interested in others, speak to them from their point of view, sincerely flatter others, seek similarity, avoid conflict, and many other things that seem obvious, but that we all routinely forget to do.

However, his methods can be manipulative and lead to shallow friendships.

We don't want awful people to exploit our weaknesses, but the irony is that our weaknesses are where trust comes from

How do you signal you're trustworthy? By trusting someone else.

• Vulnerability tells people they're part of an exclusive club.
• Not only is vulnerability effective, but it's also not quite as dangerous as you think.
• Psychology has documented the "beautiful mess effect"-that we consistently overestimate how negatively our errors will be perceived.
• The occasional screw-up is a positive.