One of the biggest myths in the National Football League is the idea that a player cannot lose his job after suffering an injury and missing playing time.

When a player goes down, there is already a backup ready to take his spot. All it takes is one injury to another player and the backup now becomes the starter.

Now, whether or not the original backup eventually becomes the full-time starter depends on the situation with the injured player.

NFL players have an average career of three-and-a-half years. It is a mistake for them to become comfortable and think they will play forever.

It is an even bigger mistake to think they are not replaceable. Whether the injury is serious or not, a football player is only one play away from being knocked out of the game – either physically or through demotion.

I think the reason this is such a hot topic in the football community is because people have different views on whether or not being replaced is fair.

To be honest, I do not know what is fair and what is not fair. That is a gray area to me.

Perhaps the only concrete reason to claim an injured player’s swapping is fair is if the newcomer provides more potential and ability at the position.

There are some players in the NFL that are unquestionably elite at their respective position.

Players like quarterbacks Tom Brady and Aaron Rodgers on offense and linebackers Patrick Willis and DeMarcus Ware on defense are simply too good to be easily replaced.

If any of these players were to get injured, their job would not be in jeopardy.

Controversies only occur when there is a legitimate brewing of tension between choosing the original player and his replacement.

The most recent controversy in the NFL involves the San Francisco 49ers’ quarterbacks Alex Smith and Colin Kaepernick.

Smith, the eight-year veteran, boasted his best season under center in 2011 after leading the 49ers to the NFC Championship game against the New York Giants. The previous six years were very up and down for Smith and the team. Many fans, including the media, had given up on him.

While his stock has risen the last season and a half, many still doubt him.

Smith was knocked out of the Nov. 11 game against the St. Louis Rams with a concussion and replaced by second-year quarterback Colin Kaepernick.

Kaepernick has started two games since then - against the Chicago Bears and New Orleans Saints - and played very well in route to winning both games.

I do not think there would be a quarterback controversy if Kaepernick did not display a different, and better, level of play than Smith had – but he has.

Kaepernick’s ceiling is unknown, but it undoubtedly is higher than Smith’s.

For the last eight seasons, I have come to understand the type of player Smith is. He is careful with the football, relies on check-downs and is not a deep-threat quarterback.

Now, this is fine and wins games, but fans want more.

Kaepernick, although relatively still unknown in his abilities, provides more ability at the position. He is currently on a hot streak and should get better each game.

Smith will lose his job to Kaepernick, but what the future holds remains to be seen.

I personally do not think it is fair. After all, Smith has been a winning quarterback for the past two seasons.

But when Kaepernick had to step up for the injured Smith, he outplayed him in every way. Kaepernick under center opens the 49ers passing offense up and creates a new, explosive dimension it lacked before.

James Heck can be reached at [email protected].