Why did the Bulls’ fast start evaporate so quickly?

The Bulls' reign as the NBA's biggest surprise barely lasted two weeks.

After starting 6-1, they've gone 3-10 since and are currently riding a four-game losing streak heading into Wednesday's game against Brooklyn at the United Center.

What have we learned about this group? Well, the longer-term future might still be bright, but success is a delicate balance for these Bulls. Missing parts or shoddy effort will flip the cart quickly.

The good news is Josh Giddey has picked up where he left off last season. He's averaging nearly a triple-double (20.6 points, 9.9 rebounds, 9.1 assists), and shooting 40% from 3-point range. He's third in the league in assists and the only guard among the top 20 in rebounds, as long as Atlanta's Jalen Johnson is defined as a forward.

Matas Buzelis has also taken a step forward in his second season. While Giddey seems to be in contention for an all-star nod this year, Buzelis has clear star potential.

There's some player development wins also, since Ayo Dosunmu and Tre Jones have shown they can be reliable rotation pieces.

Everything else, though, can crumble at a moment's notice. Coby White has played in just five of 20 games. He came back from a right calf strain, which originally happened in August, and now there's concern about tightness in the left calf.

He's averaged 24 points when he has played, but as long as he's sidelined, it's tough to tell whether White will be an ideal fit between Giddey and Buzelis, or if the Bulls should consider using him as trade bait.

The Bulls had a stretch about a week ago where the defense was abysmal, allowing 140-plus points in losses to Miami and New Orleans.

The Bulls' defense improved in the last two games, narrow losses at Indiana and Orlando. In both contests, turnovers and offensive rebounds, especially in crunch time, proved to be problematic.

“We kind of fell away from that physicality a little bit and then we are starting to regain it back now,” Buzelis said after the Orlando game.

One possible reason was a back injury to Isaac Okoro, who was brought in from Cleveland to add some defensive toughness. He's now missed five games.

Individual defense can always be difficult to measure, and one odd factoid is Okoro is last among Bulls regulars in defensive rating this season. Who's first? It's Dalen Terry, who hasn't played as much, but has also missed the last five games with a calf issue.

Terry and 6-9 forward Zach Collins were assigned to the Windy City Bulls on Tuesday to get some practice in, which is a sign both might be close to returning. Collins has not played since breaking a bone in his hand during the final preseason contest.

Backup center Jalen Smith has missed the last two games with a hamstring injury, which left the Bulls lacking height beyond Nikola Vucevic. Two-way rookie Lachlan Olbrich has served as the backup center the past two games.

Ultimately what the Bulls need is a front-line defensive presence; someone who would ideally offer some rim protection and defense against power forwards. The Bulls ended up having to use Buzelis against Indiana's Pascal Siakam and Orlando's Franz Wagner in crunch time, and Buzelis, 21, isn't physically ready for that challenge.

“I just try to stay aggressive, clear my mind, play free, be present,” Buzelis said Monday. “I had a good talk with my mental health coach telling me don’t worry about the results. Whatever happens after, it happens. You have to let it go. Don’t worry about the stats.”

Playing Buzelis at small forward instead of power forward is the big-picture goal for the Bulls. But shot-blocking big men aren't easy to find.