Oh, the things Sean will never do. Drive a car. Go to college. Ask some nice girl to dinner.
Sometimes, it's all spelled out for his parents, Bob and Peggy Best. He can't do this. He'll never do that, they're told.
But they don't like to hear it. Can't stand to hear it.
"It bothers me," said Peggy Best.
Because for all the limitations imposed on Sean by autism, there is so much he can do, and do well -- ride a bike or downhill ski or in-line skates.
And that, they say, is remarkable, considering the mental wreck he once was.
Sean Best is 17. He lives in Greensburg with his parents and attends Clelian Heights School for Exceptional Children.
He is severely autistic. It's a neurological disorder that leaves him disconnected from the world, unable to make sense of it.
He can speak, but just a little. He can read, but not at the level for someone of his age. He'll forever need someone to look after him.
But, as Peggy Best said, there are things he's capable of that others aren't. Like running in a race.
So Thursday morning, with assistance from Amy Brant, a friend and former therapist, he competed in the Latrobe-Unity Parks & Recreation's 5K Turkey Trot, along with about 550 other runners.
It was cold. The wind bit cheeks and noses and snow slushed over the roads.
But there was Sean. That he was able to run in it, and that he has been able to run in 25 to 30 other races, is an accomplishment, his parents said.
There was a time when such a thing would have been impossible for him. Just about anything would set off a tantrum. He'd bite his hands, roll his fingers. Going to dinner or sitting through a movie were out of the question.
"He was a mess," said Peggy Best. "We'd be lucky to get into McDonald's with him."
When he was 8, he started working with a group called Northwestern Human Services. Its employees set out to teach Sean how to navigate the world.
His therapy was intensive, and it involved time and positive reinforcement. Sit still for a minute and earn a doughnut. Run for a minute and earn an M&M.
The changes came slowly, but they came.
"He ties his shoes now, but it took us two years to teach him," said Brant, who has worked with Sean since he was 11. "Sometimes, the milestones don't come fast."
Running in a race was one milestone. The 2000 Turkey Trot was his first.
Peggy Best said running races was something she used to do. That, she thought, would be something good for her son, something to give him some exercise and something to get him involved in the world.
Then, as now, Brant was with him, stride for stride, guiding him along.
Even though she moved to Ocean City, Md., earlier this year, she came back to run with Sean.
"We've never had a major conversation, but he's one of my friends," she said. "Sean has taught me more than I could ever teach him."
What he taught her, she said, is that, "You can really do anything."
Peggy Best said she doesn't know whether her son has a sense of accomplishment from competing, but she sure does.
"He's a treasure," she said. "He never ceases to amaze me."
At the end of race, after he crossed the finish line in under a half-hour, his mother clasped one of his hands in hers and rubbed it.
"Good job," she said.
