Self-confidence, serenity, a sense of fears vanquished and aspirations attained. All those priceless rewards awaited Matt Stradling and Dan Stevens, and all they had to do was walk 55 feet in a straight line.

Couple of things about that: The line was actually a 1-inch-wide strip of nylon webbing, strung between rocks and fluttering in a stiff wind. And below the line, there were more rocks.

A few thousand feet below.

Stradling and Stevens, both 20, had come to the Lost Arrow Spire, a soaring monolith in Yosemite National Park in California's Sierra Nevada, to face one of the ultimate tests of a sport and art form known as slacklining.

Take the "tight" out of tightrope and you have an inkling of what slacklining is about. Although the line - the same type used by rock climbers - is pulled taut enough to walk on, it still bounces and shakes and wavers.

To stay upright on it, much less pace across it, demands focus, balance and what Stevens calls "an almost meditative state of concentration."

Not easy when you're teetering on a wisp of webbing some 3,000 feet above the Yosemite Valley.

But the discipline the pursuit demands has stoked these two childhood friends' passion for slacklining over the past year and a half. And when they both succeeded in walking the Lost Arrow line this summer, the gifts were powerful and lasting.

"For me, it was an empowering sense that I can do what I put my mind to," said Stevens, between stints of slackline practice at Orpheus Park in Encinitas, Calif., on a recent afternoon.

"That's what it comes down to. The challenge seemed so daunting before, but then once I really faced it and went for it and kind of got my head set, I was able to accomplish it."

Stradling, who lives in Encinitas (Stevens is a student at Northern Arizona University), said he learned as much from the fears and false starts and crises of confidence as he did from his ultimate success.

"That's kind of what I love about slacklining," he said. "The kind of frustration you get in not being able to do it. I like to will my way through it.

"It allows me to use strong willpower without worrying about affecting anyone else negatively. It's just me and the line."

Stradling fell twice - once as he started out on the line, and once as he started the walk back. Falling, though, is not necessarily as dire as it sounds.

On "highlines" such as the Lost Arrow Spire, slackliners wear climbing harnesses that are leashed to the line. In a fall, the slackliner also will typically grab onto the line rather than dropping to the end of the leash, although it's there as a final (literal) fallback.

In their practice sessions at local parks, where the slackline is strung a few feet above grass between two trees, Stevens and Stradling leave themselves plenty of opportunity for bumps and bruises and line-induced contusions as they try back flips and other feats.

But at a place like the Lost Arrow Spire, they have no problem relying on safety gear.

"For me, it's the difference between safe and not safe," Stevens says. "I wouldn't walk on it (there) without having that leash.

"There are some people who would, but maybe they just value their lives less. I know I have more to do in my life than just walk the Lost Arrow Spire."

Even with the precautions, making that first move onto the line was still like stepping into another dimension, the two say.

"I'm not so afraid of heights, but it's still something to overcome," Stradling said. "At first you really feel as though you forgot how to slackline. Most of the people had that syndrome, I guess."

Stevens agreed, observing that the phrase "It's just a slackline" became one of the mottoes of the Yosemite trip.

"You just look off and see that void," he said, describing how the magnitude of the endeavor tended to erase the brains of even experienced slackliners.

"For me, the webbing seemed so small. You've got these huge Yosemite peaks around, and this huge gap. It doesn't fit with logic to just see this (line) and think that's all you're going to walk on to get across."

The pair were among a group of about 20 people at the Lost Arrow Spire, which has become a slacklining mecca over the past few years. The sport itself started among climbers perhaps 20 years ago and has slowly grown to the point where Web sites and even some businesses are now devoted to it.

One of the Yosemite trekkers was Damian Cooksey, who recently set the record for the longest slackline walk, at 506 feet. Cooksey introduced Stevens and Stradling to slacklining at a church camp and has been a key reason they've embraced the sport.

"It just seemed like too big a challenge for me to face," says Stevens, recalling when Cooksey first urged him to try the Lost Arrow Spire. I was just, 'No, I can't do that.'

"And then I kind of hung out with (Cooksey) some more, and a month later he said, 'Dan, you really should think about coming. I think you can do this.' That's when I really considered it and brought it up to Matt, and Matt was all for the idea."

Just getting to the spire is an adventure - a six-hour hike carrying enough gear for a week's worth of camping. After that, rigging the slackline takes another two days (Cooksey had to climb the spire to do so).

Getting to the stepping-off point also requires rappeling down about 50 feet.

Not everyone who tried was able to walk the line. (Among those who did cross was the first female, Stradling said.) But even those who didn't succeed shared in the intensity of the experience.

"It's really interesting because it opened up a lot of bonding with the group," Stevens said. "Because people are facing really deep fears. And people are on the canyon wall supporting them."

Since their return, both Stevens and Stradling have continued their slackline practice, and have woven the sport further into their lives.

Stradling, who attends MiraCosta College in Oceanside, Calif., and works at a coffee shop, has started a business called Slacline that offers demos and instruction at parties and other events. Stevens plans to team with his brother to restart an adventure-travel service their dad ran some years ago; he also might try to sell slacklines in Chile when he spends a semester there.

Slacklining has become so integral to their way of being that in Stevens' mind, the sport's unique blend of Zen mindfulness and X-Games exhilaration can serve as a metaphor for life itself.

"If you go too far to one side, you're going to get out of balance," as he observed. "And the line may be shaking, but you've just kind of gotta let it move.

"Learn to relax, and go with the flow."

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