Defense wins championships.
The flip side of that double-edged sword is that defense can also cost you dearly. Even when you have a 21-point lead on the road and appear to be coasting toward an easy victory.
How does something so catastrophic happen? That's easy: an uncharacteristic four interceptions by the otherwise unstoppable Tom Brady (one for a go-ahead touchdown), coupled with poor coverage and tackling by the defense.
Harder to explain is how such a momentum swing occurs. How does a team that's playing so well suddenly play so poorly, and vice versa?
Co-captain Vince Wilfork was among the first Patriots to leave the visitors locker room at Ralph Wilson Stadium, so, he offered nothing to reporters. It was one of those games where you knew you probably wouldn't get a lot of answers from the just-vanquished players.
But those brave enough to face the music gave you their immediate, visceral reactions.
"It's a football game. Stuff like that happens. We have to be able to weather the storm," said linebacker and co-captain Jerod Mayo, shaking his head in disbelief. "As a defensive unit, we have to get the ball back to our offense. We weren't able to do that.
"We knew they were never out of the game ... We knew they could come back, they had that ability with that explosive offense. We just didn't execute."
"They made more plays than us. That's really what it boils down to. That's really all that matters, you know," added cornerback Kyle Arrington, who bounced back from a concussion last week to register the first two-interception game of his NFL career.
Both of those picks, however, came in the first half, when the Patriots were dominating the Bills on both sides of the ball. Momentum began to swing back in Buffalo's direction toward the end of the first half and throughout the second.
"They made more plays when they had to have it," Arrington added, "so, we've got a lot of work to do, obviously.
"Sixty minutes ... that's why you play the entire game. We just gotta do a better job of closing out, playing a full 60 minutes; a better job of playing off each other - offense, defense, special teams; a better complementary game."
For a while, both offense and defense were complementing each other quite well. Tom Brady was near-flawless in the first half, Rob Gronkowski and Wes Welker were unguardable, and the defense, led by Arrington's picks and Kyle Love's run-stuffing prowess on the defensive line, were making easy work of the Bills.
Complacency didn't appear to be the problem. New England's offense continued to try putting their foot on the neck of the vulnerable Bills defense. But Buffalo's up-front defenders were able to get their hands on some of Tom Brady's passes, batting some away and holding on to others. Remarkable, the QB finished the day with as many picks as touchdowns.
"Some days the ball gets batted in air and goes your way. Some days it doesn't. That's the way the ball bounces. That's football," a dejected Brady told reporters.
"What should be a great fun day of breaking records is totally the opposite," Welker lamented. "We have long ways to go. We have to step up across the board and understand we can't play like this.
"The turnovers killed us in the end. When we get in key positions we can't turn the ball over. We didn't play very good complementary football with each other. They were definitely a tougher team than us today."
Days like this often can't be explained, even after you go back and watch the film. Remember the Cleveland game last year? Bad days just sometimes happen, even when the day starts off so promising.
The more pressing question now is, how do the Patriots respond to this loss?
For that, the Patriots did have some answers.
"I think the main thing mentally," said frequently-victimized cornerback Devin McCourty, "is just getting back to work. We don't have time to be frustrated or disappointed after the first three games of the season. We have to keep going at it because it's a long season."
"It's one loss. It's a long season," echoed Brady. "We'll go back to work and see if we can play better next week."
"They have a good football team, and I still think we have a good football team," declared Mayo. "We just didn't play well today."
"It's going to be a long week," Arrington predicted, "but we'll come back out better for it."
They'll need to, because as their next opponent, the Oakland Raiders, showed by beating the Jets today and nearly beating the Bills the week before, they're just as capable of matching New England in a shootout.
Live by the sword, die by the sword? Today, at least, the Patriots died of self-inflicted wounds.