But finally, after all these difficult and disappointing years, Poston will take the field for the Utah Utes when they open the season at UCLA on Saturday - poised to be a dazzling featured tailback for the final season of his football career.
"To be honest, I still can't believe that I'm actually going to be playing," he said. "I have my friends contacting me every day, like, 'Are you really playing? You promise? Serious? Please don't joke around with me,' because they've been waiting years for me to play."
They have been waiting?
What about him?
Poston has had five previous seasons at two schools ruined by injuries, derailing the most promising of careers before it ever had a chance to really get started. Only a special eligibility waiver has kept his dreams alive this long, yet even now, the former high school All-American is coming off a hamstring injury that kept him out about a week of preseason training camp and resulted in junior Mike Liti earning the starting nod against the Bruins.
Through it all, though, Poston never has lost his faith that he can - for once - outrun his painful past, if only for a few glorious months.
"In all honesty, it still hasn't hit me," he said. "Until I step on the field and actually line up behind the quarterback, that's when it will probably hit me. . . . It's unbelievable."
The Utes hope it stays that way.
They put a lot of faith in Poston by not recruiting a junior-college running back to help take the place of departed workhorse Quinton Ganther, even though coach Kyle Whittingham hasn't been able to pinpoint exactly why he felt he could rely on a player who has played in only 15 games over the past five seasons.
Perhaps it was the tremendous spring practices, when Poston was completely healthy for the first time in ages and dazzled the coaches with his blazing speed and versatility. Perhaps it was simply a gut feeling. Perhaps he had few other options.
In any case, Poston will be a central figure in the offense - maybe even dictating how far the Utes go this season.
If he can stay healthy, after all, the Utes figure to have one of the nation's most diverse and potent attacks. If not? They will find out how dangerous they can be with only Liti and unproven sophomore Darrell Mack in the backfield.
"He adds a dynamic to the offense, an explosive element to the offense, that we have to have," offensive coordinator Andy Ludwig said. "Is he going to be a 30-carry-a-game back, or 25? I don't know. I don't know. But he's a guy we have to get the ball to, because he's a dynamic and explosive player."
Everybody knew that when Poston came out of Edison High School in California.
That's how he wound up at USC, ahead of a promising stable of backs that included Reggie Bush and LenDale White - players who went on to form the nucleus of the Trojan teams that won back-to-back Associated Press national titles in 2003 and 2004.
Poston was gone by the time any trophies were hoisted, though, done in first by a knee injury his freshman season, then by back and kidney problems that took more than two years to diagnose and treat properly. The Trojans never did clear him to play again, however, and after sitting out the '03 season, Poston transferred to Utah.
He played one game before suffering another season-ending knee injury in 2004, then managed to appear briefly in seven games last season after a sprained ankle and summertime bout of mononucleosis slowed him early in the year.
Now, finally, he's hoping he can forget all that.
"It's always going to be in the back of your mind, but it's not going to hinder my ability," he said. "I believe after the first game, it will all be erased. I'll establish my confidence and stuff like that, and everything will be OK."
On top of everything else, Poston is getting his shot against the rival he never knew. He had hoped to meet the Bruins during his freshman season at USC, but pushed too hard, too soon, in recovering from a knee injury, and wound up missing the rivalry game.
He knows the rivalry, though.
"I still have those feelings, like, beat UCLA," he said. "It was just like here initially. I was like, why do people hate BYU so much? And then as time goes on, you kind of realize - you kind of meet some of the alums and some of the people who are affiliated with BYU - and you kind of understand it, same as UCLA. Just being around UCLA individuals and all that, and you see people driving around there you just kind of get a feel for the whole rivalry and stuff like that. And you know? That still hasn't left me."
Neither has the faith that he not only still has something left to prove, but also still has the tools with which to prove it.
"What's been keeping me going is obviously God, and having faith in him and believing that everything happens for a reason," Poston said. "So I mean, once you look at it from that point of view, you can never be mad. You can kind of be disappointed, upset at times, in the short run. But in the long run, you realize it's just steps in your life that you have to go through."