That's what happened with a Temple University Graduate student. And he didn't think twice about helping.
This morning, Marc Schaffer was along the sidelines at football practice, where he is part of the training staff.
Yesterday, he was helping save someone's life with his bone marrow.
In 2008, Marc volunteered to become a donor, with a simple cheek swab at a campus drive that was held for a friend.
"The team was doing it, and i just wanted to sign up," he says.
He wasn't a match then, and he largely forgot about being on the registry.
But last month, he got a call that he was a match for someone else - a boy with Hodgkin's lymphoma.
Marc didn't hesitate to say yes.
"Once you get that call, it's no longer about you. It's not just the kid - it's a family, a community, everyone's affected by someone else's decision," he notes.
Head coach Matt Rhule says the whole team was excited when they found out.
"We're really proud of marc that he would do something like this," he told Action News.
So yesterday, at a local hospital, bone marrow stem cells were filtered out of Marc's blood.
He says the process wasn't difficult.
"I watched 4 hours of SportsCenter reruns and just laid there," Marc says with a laugh.
His donation also honored his friend, Misha Daughtry. She was the inspiration for the original bone marrow drive five years ago. Misha was the team's student equipment manager.
She died 2 years ago after a battle with leukemia.
Today, Marc says he feels great, in body & spirit.
"You can't put a price on how you feel knowing that your cells are going off to someone within 24 hours, so that they'll have a second chance at life," he says.
Marc told Action News he wants to wish the bone marrow recipient luck, and hopes to meet him someday.
This is Coach Rhule's first year at Temple but he says he plans on continuing the tradition of Coach Al Golden by holding bone marrow drives, so they can help save more lives.
"We're surrounded by the city, and we have a chance to give back," he says. "It's fruition off of something we did years ago here. i immediately texted al golden and let him know."
But you don't have to wait for a drive - you can sign up now at BeTheMatch.org