There are two kinds of people in the world: People who do stunts that will take them close enough to death that they can run their fingers through its hair, and people who like to watch them doing it. The first group can't wait to rollerblade down the mouth of an active volcano. The second group loves to watch in suspense, screaming "OH MY GOSH!!!" and then go home, reheat the leftover casserole, and call it a night.

Both groups recently had fun when Robbie "Kaptain" Knievel jumped over 24 delivery trucks at Kings Island amusement park, earning a world record. King Island is a historic place for the Knievel Mishpacha. It was there that Robbie's father, Evil Knievel, performed one of his most famous stunts -- jumping over 16 buses -- back in 1975.

Before heading out to the starting ramp, Knievel had a quick pep-talk with the over 40,000 people who came to see him flirt with death. "Hopefully I'll see you after the jump." He wasn't joking. His father has the world record for broken bones, after breaking them more than 40 times. He also spent 29 day in a coma after crash landing an attempt to jump the fountains at Caesar's Palace in Las Vegas.

David Blaine is another example of someone who seems unable to enjoy life unless he's hanging on to it by a thread. His most famous stunts include spending 44 days suspended over the River Thames with no food. He lost 50 pounds and needed medical intervention at the end, but he said, "The first 28 days were beautiful. I'd never throw that one away, although I did get major organ failure." He endured 62 hours encased in an ice block in Times Square and spent seven days in a coffin with no food and water.

I think his craziest stunt was his most recent. On April 30, 2008, he held his breath underwater for 17 minutes on Oprah. Afterwards he explained, "It was overwhelmingly intense. I felt my heart suffering, my lungs suffering. The urge to breathe was overwhelming." Most humans begin suffering irreparable brain damage after four minutes without fresh air. With training, you can dramatically increase that time limit, but there is still a risk of drowning or permanently damaging tissue in the brain, heart, or lungs.

Then there is Nur Malena Hassan, a 27-year-old woman from Malaysia, who spent 36 days in a glass enclosure with 3,069 poisonous scorpions. After her 17th sting she felt she had enough, stepped out of the box and started shopping in the mall where she performed her stunt.

Part of the motivation is the thrill we feel when we push ourselves to very limits of what's possible.

While these people are on the fringe, there are plenty of others who engage in very dangerous activities simply for the thrill of it. The bungee jumpers, the skydivers, the freestyle skiers and snowboarders, the extreme white water rafters and the surfers who ride out into 30 foot waves…

Back in my snowboarding heyday, I was drawn to taking runs through the freestyle park and catching airtime on the jumps. There was something intoxicating about the fear, excitement, and intense concentration you feel while speeding up a ramp that will launch you into the sky. But it all ended for me the first time I took a really bad spill. I remember lying twisted on the icy snow, in massive pain, and telling myself, "That's it, no more of this. I hope to have kids one day, and they are going to need a daddy in full working order!"

Why do some people gamble with their lives for sport? Part of the motivation is the thrill we feel when we push ourselves to very limits of what's possible. At that moment, we are living on the edge, and that causes an exhilarating, intoxicating rush of emotions. David Blaine regularly says that his goal is to show people that we are capable of doing things that are normally thought of as impossible, that by going to the edge and pushing outward we can stretch human accomplishment beyond our wildest dreams.

The good news is that we can live on the edge without hanging off a glacier or running in front of dozens of two-ton bulls. In Judaism we see all those feats of strength and physical prowess as insignificant compared to the limits we can and need to push in realm of character development.

Who is strong? One who overpowers his inclinations. As is stated (Proverbs 16:32), "Better one who is slow to anger than one with might, one who rules his spirit than the conqueror of a city." (Ethics of Our Fathers, 4:1)

When dealing with physical strength, humans are insignificant. A grasshopper can jump 30 inches. If humans could jump that many times their body length, they could cover an entire football field in a single bound, without a rocket powered motorcycle! A whale can stay underwater for two hours at a time and camels can live for 50 days without water. Our achievements in the physical realm are nothing compared to those of the animals around us. Our true strength lies in our character.

We can get our thrills by pushing ourselves to become better people than we ever thought possible.

We can get our thrills by pushing ourselves to become better people than we ever thought possible, and seeing the accomplishments we never believed possible. We can become more involved parents, more attentive husbands, more active Jews, and more caring humans than we think possible. Challenging ourselves with specific milestones that seem beyond our capabilities, and then striving mightily to reach them can be more cutting edge than sky-diving. Fighting with our natural negative inclinations and transforming ourselves into a new human being is harder than standing in a slab of ice for a week!

Rabbi Yisrael Salanter the father of the Mussar Movement, a movement focused intensely on character building, said that changing even one negative character trait is more difficult that learning the entire Talmud. The training, conditioning, focus, belief in oneself, willpower, and endurance necessary in building a better human are the most limit-pushing exercises available to mankind.

Let's try to focus on one character trait we would like to change, and write down a plan of action to utilize our summer to train ourselves in that area. Real strength is not in stunts, it's in self-development; not in muscles but in mastery -- of ourselves.