No matter how skilled or talented an offense is, it all comes crashing down without proper blocking.
The Rams learned this in Super Bowl XXXVI.
The Patriots learned this again in Super Bowl XLII.
So as the preseason moves into its second weekend, and teams begin looking around at their needs, offensive linemen come to the forefront.
Already, some teams (like the Jets, possibly) are noticing that their current lines might either not be complete or are not completely healthy.
In any case, many veterans are still available in free agency. Here's a look at a few of the best ones (not ranked in a specific order).
Seubert helped the Giants win Super Bowl XLII. However, he apparently didn't fit into their future plans, so he was cut.
What he offers is experience at the highest level and a track record of blocking for great running games.
At only 32, he probably still has some NFL left in him.
For anyone who's been paying attention to the Vikings' offseason moves, they'll know the story behind this one.
McKinnie, a former standout at Miami, was cut by the only NFL team he's ever played for because he showed up at camp way overweight, at nearly 400 pounds.
It's interesting how quickly a team's opinion of someone can change. Not that long ago, he was seen as one of the best players on the team. Now he's as expendable as a used car.
If he can get himself back into shape, there's no reason why McKinnie couldn't be a valuable addition to a team.
Another ex-Giant who was a member of the Super Bowl XLII team.
He's not as young as some of the other guys on this list (34), but he is one of the only three-time Pro Bowlers who's available.
In New York, he proved himself smart and tough, blocking against some stiff NFC East competition.
Aside from the fact that Davis is probably one of the strongest men in America, he's another 32-year-old, unemployed guard.
Released by the Cowboys, he matches O'Hara as a former three-time Pro Bowler.
He does commit his fair share of penalties, but no one can doubt the talent of the former second overall pick from the 2001 draft (taken by the Cardinals).
He was plagued by injuries in his final seasons in New England, and was eventually replaced by the Patriots.
If he can prove that he's healthy, he might be a good value player for a team that's looking to make a run. After all, since he played for the Patriots, Kaczur certainly knows what it's like to play in big games.
Another veteran who might have more mileage left in him.
The clock is certainly ticking on Waters, who's 34 and not getting any younger.
Yet he's quietly been one of the most decorated linemen of the last decade, being named to five Pro Bowls and blocking for players like Priest Holmes, Larry Johnson and, most recently, Jamaal Charles.
If your team is looking for size (or height), then Starks is the guy.
At 6'8" and 370 pounds, he's a mountain of a man.
And like some of the others on this list, he's been in big games (and won Super Bowls).
Starks is also on the younger side compared to the rest of this list at only 29 years of age.
At 31, Stinchcomb has already had a hell of a career.
He started 80 consecutive games and was named the Saints' "Man of the Year" in 2008.
Yet after helping Drew Brees and the rest of the team to a Super Bowl, Stinchcomb ran into injury problems last year and was released.
He's the classic case of a reclamation project waiting to happen. Some team is going to swoop in and sign him and he'll probably give them a few solid seasons.
Kidding! You didn't really think I'd endorse Flozell after what I've already said about him, did you?