How we make friends is a mystery.

But what we do know is that lifelong friendships have what experts say are the necessary components — commitment, shared interest and flexibility — especially in a world where adults frequently are too busy to make friends or seem to have forgotten how.

Too often suspicious of newcomers, grown-ups could take a lesson from children, who embrace new faces without making judgments.

William Rawlins, a professor at Ohio University and the author of the book "Friendship Matters" (Aldine Transaction, $26.95) has been studying friends and friendship for 30 years. He knows common interests, such as being a military wife, are a foundation for building friendships.

Another factor in finding a friend is a commitment by both people to spend time together.

Time, Rawlins says, is one of the most important factors in creating and maintaining a friendship, but it's something not many people have.

When Rawlins sees people prioritize their time, family, work and romance are at the top of the list. Friendship is usually near the bottom. That's why in a search for new friends, it's important to start where you're already spending time.

The friendship of two kindergartners brought Phoenix, friends Vicky Okamoto and Diane Cylwik together 16 years ago. Their little boys always wanted to play together, so the women soon began exchanging pleasantries, on the phone and at their front doors.

As often happens, the boys grew apart by the time they got to high school, with Tristan Okamoto preferring the arts and Scott Cylwik choosing sports. Their mothers' bond grew stronger, however, fueled by a common interest that's enriched their lives and cost nothing: a daily walk through their neighborhood.

"We've decided we have to retire in the same place," says Okamoto, a 53-year-old elementary school clerk, "because we're going to be doing this till the day we die."

For the past 11 years, she and Cylwik, 52, have walked two miles nearly every day, except when vacations or illness interfered, taking 30 minutes out from raising families and working jobs to nurture their relationship. They've trekked before dawn and after dark, in wind, rain and heat but, alas, never snow.

"Kids just want to play," Cylwik says, "but we're more in a rut, set in our ways."

Billie Speed and Jane George have no idea how it happened.

"I don't know. How did we become friends?" Speed, 85, asks her longtime friend and fellow resident of the Montecito retirement community in Peoria, Ariz.

"I can't remember, Billie!" George, 80, replies, shaking her head and laughing.

That invitation is the real beginning of friendship. Rawlins has discovered a pivotal move in creating friendship is when someone decides to spend time together that they're not required to. It's the first lunch together outside of work or the first shopping trip that sends the message: "Will you be my friend?"

There's a window when two people sense they can be friends. Extending an invitation too soon can appear needy, but waiting too long to try to get together can be awkward.

"People want to make friends," Rawlins says, "but put so much pressure on themselves. Relax a little bit."

When you finally do meet up with friend material, it's important to make small talk part of the process. The more you talk with someone, the more important information you tell them, what BJ Gallagher, a Los Angeles sociologist and author of the book "Friends Are Everything" (Conari, $15.95), calls developmental exchange. If you start with the big, intimate information right away, chances are you'll scare away your potential friend by seeming too clingy.