Problem is, you can usually find him in the gray area between those two points. So making any type of permanent conclusion on just what the Chiefs have in Cassel becomes extremely difficult.
Despite his relationship with head coach Todd Haley, Cassel is the type of player coaches love. Without the obvious size or arm-strength advantage, he's become an NFL starter by doing the little things and playing smart.
He's tough as nails, too. Last year, less than two weeks removed from an emergency appendectomy, Cassel led his team to victory on the road against a playoff-hopeful St. Louis squad in a game the Chiefs would later realize they had to have.
So the intangibles are there.
Sunday, with their backs against the wall, the Chiefs allowed Cassel to lead the way for their first victory since early last December, and it's no coincidence that victory against the Titans was the last time he resembled anything close to an NFL starting quarterback.
Cassel looked poised, eased through his progressions without panic, and with the game on the line was at his best. It wasn't hard to envision — with a healthy Jamaal Charles, Jonathan Baldwin, and Tony Moeaki — this team winning important games in December and January with Cassel at the helm.
But then there's the other side to this.
In a much more important divisional game a week before, Cassel looked dismal against a San Diego team that appeared disinterested in winning. The Chiefs didn't gain a first-down until the second half. Still, somehow, there was an opportunity for victory in the game's closing moments.
Cassel folded like origami.
Had the quarterback played even half as well in San Diego as he did Sunday at Arrowhead, the talk around Kansas City would be less about who the team will draft in April and more about the strong likelihood of having a winning-record coming out of the bye week.
This is where you have to sympathize, at least to a small degree, with the decision facing general manager Scott Pioli this offseason. Cassel is still relatively young and developing. He's never had two legitimate NFL wide-receivers to throw to while in Kansas City.
And parting ways with a quarterback with a career winning-record just a year removed from a Pro Bowl season isn't exactly the obvious decision, especially after you consider the injuries to the starting running back and tight end.
See, there's so much gray here.
On the one hand, you have a quarterback whose teammates credit the passion he displayed during an impromptu halftime speech as an explanation for the team's determined second half play Sunday.
On the other, you have a fanbase more concerned (even after Sunday) with the appropriately titled #Suck4Luck campaign (rooting for the team to lose in hopes it will be awarded the first pick in next April's draft so it can select the most-hyped college quarterback since Peyton Manning, Stanford's Andrew Luck), than with cheering for the team in its current form.
Sunday was by far Cassel's best performance since the Charlie Weis-to-Florida news surfaced. Was it progress after a rough adjustment period that included a lockout? Or when the schedule gets tougher and the games more meaningful, will Cassel and all his mediocrity rear their ugly head once gain, much like we saw last January?
Again, the gray.
Regardless, next year's draft will be quarterback-heavy. The rest of this season will be an unofficial audition for Cassel to buy a few more years in Kansas City.
And the irony is that — because of a potentially worse draft position — by playing well Sunday, the quarterback may have hurt his team's chances in the future more than help them.
Or, it's possible, Sunday was a major step forward for Cassel.
Just depends on which side of the gray you're on.