The ball is the same shape and the field is the same size, but there is not much else that is the same between college football and the NFL -- and count Chip Kelly, fired Tuesday after three seasons with Philadelphia Eagles, as the latest coach to find that out the hard way.
History tells us the club of coaches who successfully made the leap directly from college football to the NFL is one of the most exclusive clubs there is.
Paul Brown did it more than a half-century ago.
Jimmy Johnson did it a quarter-century ago.
Go ahead. Name another successful coach -- including some of the great ones -- who came into the NFL directly from a college head-coaching position, without recent NFL experience, and really succeeded.
Not Steve Spurrier.
Not Dennis Erickson.
Oh, there have been some who had minor successes, notably Barry Switzer, who won what should have been Johnson's third Super Bowl with the Dallas Cowboys. But generally speaking, college coaches who made the jump and succeeded worked in the NFL before becoming a college coach, and had not been out of the league for long, like Jim Harbaugh and Pete Carroll.
In fact, Switzer and Johnson are the only Super Bowl-winning coaches who never cut their teeth as NFL assistants.
Kelly, however, was a victim of his own ego. He believed a system that worked in college, with superior athletes playing at a faster pace than most teams, would translate smoothly to the NFL. He failed to grasp that every team in the NFL had great athletes and that the players were not necessarily interchangeable parts, as they frequently are in college.
As an offensive-minded coach, he surely should have known better than to throw away a receiver like DeSean Jackson and a running back like LeSean McCoy, even if he could replace McCoy with the NFL's rushing champion. The history of teams that achieve success in the NFL is that they understand how players fit certain systems; to this day, there are those who believe we might never have heard of Joe Montana if he hadn't been fortunate enough to play for Bill Walsh.
Of course, Kelly had a partner in crime -- call it footballcide -- who allowed him to do whatever he wanted with an organization that, under president Joe Banner and coach Andy Reid, had been one of the most stable in the NFL for a decade.
That partner was Jeffrey Lurie, the Eagles' owner, who first tossed aside Banner, his long-time buddy, and then Reid, because he wasn't satisfied with all those repeat trips to the NFC championship game if he couldn't raise a Super Bowl championship banner in Philadelphia.
Well, isn't it interesting that Reid, now in Kansas City, coaches a team with a nine-game winning streak and a spot in the playoffs while the Eagles are embarking on another coaching -- and general manager -- search.
Saban's history, as he goes for another national championship at Alabama, is perhaps most instructive. He coached for four years under Bill Belichick at Cleveland, and in today's game, it's hard to conceive a stronger background.
But Saban was gone from the NFL for 10 years when he took the Miami Dolphins' job in 2005 and actually had the chutzpah to say he structured his programs at Michigan State and LSU after the NFL. With the Dolphins, Saban gave up before the end of his second season to return to college football.
Mike Holmgren, one of a handful of coaches to take two franchises to the Super Bowl, once explained the difference in how a coach can control his team.
"In college, the players will do anything you want them to," Holmgren said. "(They) are worried about classes and their scholarships and then looking forward to the NFL in some cases, and what you say goes. I don't think it's ever that easy in (the NFL)."
Ira Miller is a national columnist for The Sports Xchange. He is an award-winning sportswriter who has covered the NFL for more than four decades and is a member of the Pro Football Hall of Fame Selection Committee.