It's one thing to think your young running back has the stamina for 16 weeks. It's one thing to believe he'll be tough enough to fight through the dings as the season grinds on.
It's another thing to see him do it. And as the 2010 season enters its final stretch, the Eagles have seen LeSean McCoy do it.
Late against the Giants three games ago, McCoy surpassed the 195 season touches he had as a rookie in 2009. Since then, he has shown no signs of slowing down.
He came back with 120 combined yards the next game at Chicago, and tacked on 130 against the Texans Thursday.
After last season, "the number-one thing was getting stronger physically, and he worked on that very hard, came back stronger, didn't lose any of his speed or flexibility," head coach Andy Reid said. "And then he studied. There's more than just getting the ball and running to a spot."
Along the way, McCoy has joined quarterback Michael Vick as the Eagles' most consistent offensive threats. Just as impressively, McCoy has displayed the grit needed to thrive as a No. 1 back, fighting through a broken rib early in the season and a shoulder injury that has had him on the injury report for the last three games.
"He's very tough," Reid said, even though McCoy "comes across like your little brother."
McCoy, 22, is still the youngest Eagle on the roster. He was born 11 days after rookie safety Kurt Coleman.
"He's a happy, happy guy," Reid said. "Always smiling. Always teasing people. Underneath all that is a tough, competitive, very skilled player. You can overlook that if you're just hanging around with him."
McCoy, like his mentor, Brian Westbrook, has become an expert at screen passes, allowing him to remain a central cog in the offense even as the team has leaned heavily on the pass in recent weeks.
If McCoy is not yet at Westbrook's level on screens, "he's surely getting there," Reid said Friday.
McCoy showed that against Houston, taking screens for 16 and 40 yards. On both plays, he started to the left as his blockers wiped out would-be tacklers ahead of him, then slashed right.
Most eye-popping are his receiving numbers. McCoy has 67 catches for 534 yards and two touchdowns. Those are in addition to 823 rushing yards (a 4.9-yard average) and seven touchdowns on the ground.
What makes McCoy so dangerous catching the ball is that he often finds himself in open space, where he usually makes defenders miss.
"It's a natural feeling. You see a guy, and you know what you are going to do," McCoy said after the Eagles' 34-24 win over Houston, in which he had eight receptions for 86 yards and a score. "You're just trying to get past them. All I need now is that extra burst to get me to that end zone."
Studying also helps there. Reid said McCoy had benefited from reading defenses - understanding a lineman's responsibility based on how a linebacker sets up - then allowing blockers time to reach their assignments.
McCoy has done the small things, ably blocking when called on to pick up linebackers and to chip linemen, and the big ones: He leads the Eagles with nine touchdowns.
With 1,357 yards from scrimmage, among the best in the NFL, McCoy is on a pace for 1,809 total, which would be the sixth most in Eagles history. To get there, though, he'll need to maintain his durability.
So far, he has answered every challenge.
After McCoy's solid rookie season, the Eagles thought he could carry a heavy load this year. Twelve games later, they know he can.