That maxim is especially true in the NFL, where the salary cap, draft order and other rules impose parity and leave even great teams with some liabilities.
Take the Green Bay Packers and New England Patriots, two of the best teams in the NFL, ones the Eagles aspire to match, but who ranked 31st and 32d, respectively, in yards allowed heading into Monday night. Or try the NFC West champion San Francisco 49ers, who have a middling offense - 15th in scoring - but compensate with one of the NFL's best defenses.
Every team enters a season with a few definite holes and a few gambles that could go either way. They hope their known strengths outweigh the firm weaknesses, that most of the potential problems work out in their favor and that the ones that do go wrong at least avoid the worst-case scenario.
The 7-8 Eagles, though, faced problems in each area: Their obvious weaknesses turned out to be as bad as first feared, their biggest strength wasn't good enough, and several areas of uncertainty went negative.
Some of these problems we could see coming, raising questions about why they weren't addressed. Others were surprises that coaches failed to fix. And one big risk turned against the Eagles.
With their playoffs hopes officially dashed, here's a look at the biggest on-field flaws that contributed to this disappointing season:
Turnovers. You've heard this one over and over, but it's so significant it bears repeating.
With all of the Eagles' offseason changes, the one piece that seemed sure to have a big year was the offense, which returned all of its major weapons and improved on the offensive line. With LeSean McCoy having a breakout year, the Eagles moved the ball up and down the field. But they gave it up at a reckless rate that prevented the offense from scoring enough to compensate for expected defensive woes.
In New England and Green Bay, sharp offenses cover defensive liabilities. Led by Tom Brady and Aaron Rodgers, the teams rank fifth and second in interceptions as a percentage of pass attempts and third and first in scoring. San Francisco, even with up-and-down Alex Smith at quarterback, is first in interception percentage.
With 10, 12 and 16 giveaways, the 49ers, Packers and Patriots have the fewest in the NFL.
The Eagles' 36 turnovers are tied for the most in the league and they rank last in interceptions as a percentage of pass attempts.
The Eagles still rank ninth in points per game, with 24.1, but they've needed just a little more. Five losses were decided by seven or fewer points. Just one more score in any of those games and the Eagles would still be alive.
Defensive inexperience. If the turnovers were tough to predict, many saw this issue coming from miles away. Most people questioned the Juan Castillo hire and the plan to start an inexperienced, lightly regarded group of linebackers. The linebacker situation was even more worrisome considering the added run responsibility they had behind a defensive line focused primarily on rushing quarterbacks.
The problems were as bad as feared, as the Eagles defense was outmaneuvered late in games and run liabilities crushed them early.
Two lasting images of the season will be Atlanta's Michael Turner breaking off a 61-yard run in Week 2 and San Francisco's Kendall Hunter running for 14 yards on third-and-7 in Week 4. Both were in the fourth quarter. Both set up game-winning touchdowns. With a stop in either situation, the Eagles might make the playoffs.
The linebackers and defense improved, but too late.
Quarterback play. When the Eagles extended Michael Vick's contract, the question was which version would show up in 2011: the one who mesmerized the NFL for much of last season, or the one who sputtered at the end?
The answer should go under the category of a question mark that tipped against the Eagles.
For much of the year Vick has been closer to the player who dropped his last two starts last season than the one who at one point won six out of seven. Consider: Rex Grossman has thrown the same number of touchdowns as Vick (15) in the same number of starts (12).
Vick has accounted for 16 of the Eagles' turnovers and concerns about injuries proved valid. With a playing style that involves extending plays and taking added hits in and out of the pocket, Vick missed three games and failed to finish two others. The Eagles went 1-4 in those games.
He ranks 20th in the league in completion percentage and is tied for 17th in touchdowns and 21st in interceptions.
Some gambles paid off. The remade offensive line, with a new philosophy, three new starters and a career guard moved to right tackle, has been a major positive.
The new look on the defensive line provided a hellacious pass rush.
Rookie kicker Alex Henery, despite two costly misses against the 49ers, had a strong year overall and looks like he might contribute for years to come.
But those pluses weren't enough. No one gets everything right, but for the Eagles, too many bets turned bad and the good parts weren't good enough.