That's what Foles has been for Lazor during the last seven months. Lazor has watched Foles become one of the NFL's most productive quarterbacks this season, working with the 24-year-old passer every day. Lazor's entire focus is on the Eagles quarterbacks. So when the Eagles struggle with "quarterback instability" or flourish with Foles' proficiency, it is a reflection on Lazor.
Lazor said he did not enter the season with any expectations of what Foles could be, but he also said there's more to Foles than what we've seen. Foles has made only 11 starts, so Lazor insisted that any evaluation would be incomplete.
"I still don't put a ceiling on what he could be," Lazor said.
The coach said he needed to wait to see Foles play in games to form expectations, and Foles' stretch of three consecutive wins with 11 touchdowns and one turnover is an indication of the quarterback's development. When Lazor was asked what he's learned about Foles, though, he did not talk about the production.
"The biggest thing that you don't know about a quarterback is the stuff that shows up on game day, which is his demeanor on the sideline and his ability to see," Lazor said. "Some quarterbacks can come to the sideline and can't tell you what happened out there, and some quarterbacks can come and tell you exactly where the defense was, how they turned their hips, who jumped the route. Those are the things you don't know until you go through it. Nick's done a great job of communicating on game day and seeing what the defense is doing."
That ability allows Foles to learn as the game progresses. Lazor said Foles does not necessarily need to wait to review game film to make an adjustment. What he sees on one drive can be applied to the next drive.
The week that seemed to require the biggest adjustment was leading up to Foles' seven-touchdown performance against the Oakland Raiders. He came off the worst outing of his career and a weeklong absence because of a concussion.
Lazor said that week was no different from other weeks, but he called it the "best example of weekly preparation showing up on game day." After the game, Lazor said, it was easy for the quarterbacks to trust their preparation and their studying of the opponents' tendencies.
Lazor said mistakes have been repeated since that game, but they might not be as apparent because they're not becoming turnovers. And the way Lazor measures Foles is different from the way fantasy-football owners might view him.
"I think he's at the beginning, and his stats have been very good, but we really don't focus on the stats," Lazor said. "We focus on 'How did he play?' "
The example Lazor gave is accuracy. He doesn't judge accuracy by whether the ball is caught, but by where it's thrown relative to where it's supposed to be thrown. So a crossing route must be one foot in front of the numbers, or the screen pass might be thrown to the shoulder pad.
On Tuesday, the quarterbacks worked on basic plays that are likely to be called multiple times throughout the season. Lazor said he can learn a lot by how a player approaches that kind of preparation during a bye week.
"If you're going to play at this level for a long time and be good, you've got to take enjoyment out of that work, because you have to say, 'This is how it's going to happen on game day, this isn't just drudgery,' " Lazor said. "You can't let things seem mundane to you."
Lazor continues to raise the standard for Foles, and there are nuances of the position that cannot be forgotten just because of the statistics. Lazor said "a bunch of things" in Foles' fundamentals can be improved. They drill moving in the pocket, keeping the left shoulder and left hip upfield, and securing the football, among other mechanics.
The work, Lazor insisted, is never completed.
"From the outside, it's easy to say: 'What can he do better?' " Lazor said. "From the inside, we have a lot of work to do."