Everyone "knows" there are differences between how women and men have friendships with the same sex. Guys have buddies, women have BFFs. Women have emotional attachments, guys have someone to go to the game with. Greif has taken interviews with 400 men about their friendships, and comes to the conclusion that while, yes, there are differences, a man's friendships can be as deep and lasting as a woman's, and those strong relationships help men have longer and happier lives. He breaks men's relationships into four categories--Must, Trust, Just, and Rust--that range from the person you "must" share news with as it happens, to those relationships that come and go, being picked up where it left off the last time you caught up with each other ("rust"). As you go through the book, reading the examples from the many interviews (subjects ranged in age from their 20s to their 90s), you begin to catalog your own friendships into must, trust, just, and rust. Greif also interviewed more than 100 women, looking for similarities and differences, and has put together key elements that can help make relationships stronger, that in turn helps both men live longer, less stressful lives. Which, of course, keeps the friendship alive longer.