Scott Rigsby, who in 2007 became the first double-leg amputee to cross the finish line on prosthetics in the Hawaiian Ironman World Championship Triathlon, urged students at Grace Christian Academy Thursday morning to start with a goal and go after it.

The Hawaiian Ironman, which consists of a 2.4-mile ocean swim, a 112-mile bicycle ride and a 26.2-mile marathon, is the sporting world’s most grueling and prestigious competition.

Grigsby’s book, “Do the Unthinkable,” chronicles how he became a world-class athlete after losing his right leg in a terrible motor vehicle accident at the age of 18 and later had his left leg amputated,

“All of us are on an unthinkable journey,” he told the Grace students. “While I overcame obstacles to finish the Hawaiian Iron Man World Championship Triathlon, it’s not about my story. It’s about God’s story.”

“With God’s help, today’s unthinkables are tomorrow’s realities. He asks you to join his story because it will radically change your life,” Rigsby said.

Rigsby talked about how uncertainty, doubt and fear of failure often comes out when you are going after your goal.

“You need to set your goal and step out and go after it,” he said. “Fear of the unknown often brings uncertainty and doubt, but you must still step out and try it.”

Rigsby, who lives in Atlanta, said things were looking very bleak in the fall of 2005 when he asked his mother, a devout Christian lady, to pray for him.

“When my mother prayed for me it suddenly felt like a burden had been lifted,” he said. “Right then and there I told God that if he would open a door for me I would walk through it. … The door he opened was the opportunity to train for and complete in the Hawaiian Ironman World Championship Triathlon, and I walked through it and obtained success.”

Rigsby said competitors have to complete it in 17 hours or less, and he completed it in 16 hours, 42 minutes and 16 seconds.

“I was getting a little frustrated training at home in Atlanta, so I went over to Hawaii three weeks before the event to train on site,” he said.

“When the competition began, there were 1,800 athletes in the bay. At the pre-Ironman banquet I received the Ford Survivor Everyday Hero Award. I was very surprised when they called my name.”

“A lot of adults let their dreams pass them by. Because I had a great family and support team around me, I was able to live mine,” Rigsby said.

Rigsby has founded the Scott Rigsby Foundation, which is designated to inspire, inform and enable the physically challenged with loss of limb or mobility to live an active lifestyle.