Well, if you think that way, recent history says you're likely to be wrong.
Seven of the past 10 title winners finished the regular season in the top five in defensive rating.
Miami isn't having a horrific defensive season, currently ranking 11th in defensive rating. However, it's clear that defense wins championships in the NBA, and the Heat just aren't playing championship-level defense.
There's no way around it: Miami has to focus on fixing their issues on that side of the ball if they are to repeat last year's title.
What the Heat have been known for throughout the Big Three era is their incredible intensity on defense. Using their elite athletes, like LeBron James, the Heat have swarmed opposing ball-handlers and forced them into mistakes (third in turnovers last season). That's one of the reasons the Heat were able to continue the trend of elite defenses winning NBA titles (fourth in defensive rating in 2011-12).
But that intensity just hasn't been there on a consistent basis for the Heat, and the team's turnover ranking has fallen to 11th in the 2012-13 season.
The reason for that loss of intensity seems to be pretty simple to figure out: The Heat don't want to overwork themselves during the regular season, so effort has suffered.
While that sounds good in theory, there is some danger to be found here because the Heat have been successful with this style of play.
Miami can't let their 28-13 start and top spot in the Eastern Conference fool them into thinking that they are talented enough to win it all with this amount of defensive effort being exerted.
A great offense just won't be enough. It might be enough to win the East, only due to the lack of other talent in the conference, but the Heat will lose in the NBA Finals if that's all they have.
That's because each of the top three teams in the Western Conference is capable and willing to dominate on both ends of the floor.
The Oklahoma City Thunder (first in offensive rating and ninth in defensive rating), Los Angeles Clippers (fourth and fifth, respectively) and San Antonio Spurs (fifth and fourth, respectively) are enormous threats to the Heat, even when Miami is playing top-notch defense, let alone when they're not.
The Heat need to prepare their defense to face those great teams, and that goes beyond just fixing effort. Miami has to start using defensive-minded lineups more often.
That means giving guys like Udonis Haslem (19.3 minutes per game) and Joel Anthony (10.5) more minutes and leaving someone like Rashard Lewis (who seems to have re-entered the rotation lately) on the bench.
Haslem certainly isn't the player he once was, especially on the offensive end, but he's still a tough defender and plays with as much energy as anybody.
Take a look at the difference in the Heat defense, per 100 possessions, when Haslem is on the court as compared to when he's not, according to 82games.
As for Anthony, his defense is likely the only reason he's still in the league, considering his ineffectiveness on the glass and scoring-wise.
Anthony's held opposing centers to a stellar 12.6 PER. Watch some of his work from the 2011 playoffs on the defensive end. Few guard the pick-and-roll in the NBA better than Anthony.
The reduced roles for Haslem and Anthony aren't coincidental. They have to with Miami's commitment to playing small ball. Both Haslem and Anthony just aren't of assistance in terms of floor spacing.
But while playing within the small-ball system or even potentially going away from it at times, Miami needs to remember why they've been able to have such great postseason success over the past two seasons.
Defense before offense.
If they don't, the Heat will be in for a tough time come June.