After the Celtics' 16-game win streak finally came to an end Wednesday in Miami, Al Horford made an interesting observation: "We have to play offense harder," the big man said. "I think that is the best way to describe it." 

You don't often hear that kind of critique about offense. Defense, sure. Effort is constantly being questioned on the less-glamorous end. But with offense, we tend to assume effort and focus instead on skill, execution and shot selection. 

If you watch the tape, Horford has a point. Take a look at their first offensive possession in the loss to the Heat. 

The only thing good about this play is Kyrie Irving noticing Goran Dragic was cross-matched in transition on Jaylen Brown, who he shouldn't be able to cover in the post. So Irving goes to it. The problem is that Brown doesn't notice the same thing at first, which is why the shot clock is already down to 14 before he heeds Irving's call and receives the first pass of the possession. That's 10 seconds before a single pass, or even a semblance of offensive movement, is initiated. 

From there, not a single player off the ball moves. Nobody cuts. Nobody back screens. Nobody does anything. Boston is conceding to a single-pass possession based entirely on this mismatch, even though the Celtics rank 24th in the league in iso offense, via Synergy. Brown could salvage the possession by at least forcing Dragic to guard him in the post, but instead he merely faces up and settles for a nonchalant, contested jumper. 

That is not playing offense hard. 

Compare that to this next play, where Brown finds himself in the same exact situation -- being guarded by Dragic, only this time it's late in the fourth quarter and the Celtics are in the middle of another one of their late comebacks, so the energy is at an entirely different level. Brown does not hesitate to go right at Dragic. 

If you watch that play again, you'll also notice that after Horford makes the entry pass, he doesn't stand still. Instead, he screens Jayson Tatum's man, Tyler Johnson, which frees Tatum up for a kick-out three. Johnson has to respect that shot, and in coming out to Tatum, he leaves Brown to operate one-one-one in space. That's a subtle move by Horford, but it's effort. It's urgency, something the Celtics -- who defend with so much of it -- haven't been showing enough of on the offensive end until their backs are against the wall. 

Now, back to the first half when the Celtics were just going through the motions. 

In this next clip, again, almost 10 seconds have evaporated off the shot clock before Horford receives the first and only pass of the possession, and still he's buried in the deep corner with a good defender in Justise Winslow guarding him. No one moves, and Horford ends up taking a bad shot.

Lethargic possessions like this are at least part of the reason the Celtics rank 21st in half-court offense, via Synergy. They're bad in isolation and even worse when it comes to cutting (28th in the league), which is a relatively dependable indicator of offensive effort. Next time you watch the Warriors, watch how hard they cut to the basket. Back-door cuts. Daylight cuts. Everything.

 And it's not as if the Celtics aren't capable of executing.

With the players it has, Boston shouldn't be anywhere near the worst cutting teams in the league. The Celtics have the shooting to space and concern opposing defenses. They have great athletes and finishers in Brown, Tatum and Irving. And they have one of the best passing big men in the game in Horford, who also pulls bigs away from the basket with his 3-point shooting ability. 

Again, this is just effort and a commitment to remaining active, on and off the ball, through the whole possession. This is what Horford's talking about. In the big picture, not doing this consistently is how Boston has found itself facing a double-digit deficit seven times this season, including each of the last four games. Too often they're having to survive on late-shot-clock shots going in after they run 20 seconds of halfhearted offense. Like this:

Again, this was the second quarter of Wednesday's game, before Boston got desperate. Again, when the first pass of the possession was made there were just 11 seconds left on the shot clock. Thirteen seconds to initiate your offense? And then still, nobody moves? Nobody cuts? When Tatum can't get off a shot, the possession is more or less a bust after one pass. That Smart ended up bailing them out with a last-second jumper is fool's gold. The Celtics are being propped up by the fact that they rank third in the league in short-shot-clock (less than 4 seconds) scoring, but that is not something you want to depend on long term. 

They certainly don't depend on it as heavily when they find themselves in these second-half holes, so you know they're capable of picking up the energy. Watch this next late-game clip and how all five players move from the first pass on. 

That is playing hard on offense. Every player is forcing defensive reaction, passes are crisp, drives are decisive and assertive, and it's not a coincidence that this possession happened late in the game, when Boston was down. The best offensive teams don't pick and choose when they play with urgency. After the loss, Celtics coach Brad Stevens called the 16-game win streak "a little bit of a mirage," and what he's getting at is some of the things floating the Celtics at the moment are not sustainable.

"We know we have to get better," Stevens said. "When we're locked in and we're executing, we're pretty good. However, we go through too many lulls when we're not."

It's not to say that a ton of good things can't be taken from this streak. No matter how it goes down, 16 in a row is 16 in a row. The defense is a rock. Irving is going to be there in the biggest moments. Stevens was also quick to point out the fight of his team, calling it "incredible" that Boston was able to trim Miami's 16-point fourth-quarter lead to one with less than three minutes to play. 

Indeed, there are two ways to look at all these comebacks: Either they inspire confidence because you know you're never out of a game, or they bring about concern that you're getting in these holes in the first place. For Boston, it sounds like it's a little of both. Stevens isn't going to settle for the slow starts forever, and the Celtics are too good to need these rallies constantly.

"I'm proud of the group," Horford said. "It's very remarkable [what we did]. With this streak, it wasn't like we necessarily dominated. But the will of this team is something people have to take into account."