‘We’re going to figure it out,’ Walton says of up-and-down Lakers. But when?

Those heady days of November, when a young and frisky Lakers team appeared to be far ahead of its rebuilding schedule by finishing the month with a surprising 10-10 record, seem like a distant memory as December comes to a close.

Another lackluster second-half effort against the lowly Dallas Mavericks on Thursday night at Staples Center led to the Lakers’ 14th loss in 16 games in December and dropped them to 12-24 overall, the seventh-worst record in the NBA, entering Sunday night’s game against Eastern Conference power Toronto.

The excitement and optimism of November, which featured a 117-97 victory over Golden State and a 111-109 win over Oklahoma City in which Nick Young drained a clutch three-pointer with five seconds left, has given way to a series of blown double-digit leads, defensive breakdowns, mental lapses and repeated mistakes.

With that has come disappointment, frustration and self-doubt.

In the wake of that Nov. 4 win over the Warriors, rookie forward Brandon Ingram declared, “I think we can make a push in this league, and not wait.” In that same locker room Thursday night, Young said, “We have to figure it out, or we’re going to be the doormat Lakers again.”

Young speaks from experience. He’s in his fourth season in Los Angeles, and the first three resulted in lottery-pick records of 27-55, 21-61 and 17-65.

Rookie Coach Luke Walton was a Golden State assistant the past two years and a development league coach in 2013-14, but he was around enough losing teams as a player to know that the Lakers have reached a critical point in their season.

“I told them we’re going to be fine, we’re going to figure it out,” Walton said of his message to his team Thursday night. “‘When’ is the question. How much does it mean to us right now, to figure it out this season, or do we want to wait two or three years, as natural development happens?

“We’ve proven to ourselves that we’re capable of beating anybody in this league when we’re competing and playing defense and sharing the ball on offense. We have it within us to make that improvement sooner rather than later. But a lot of it has to be an individual desire to want it now.”

Perhaps the Lakers got a little too full of themselves after their early success, or maybe this is just a big break in the learning curve, but they’ve clearly regressed over the past month.

Praised for their intensity and effort for the first 1 months of the season, the Lakers didn’t put up much of a fight in the second half of Thursday night’s 101-89 loss, scoring just 32 points in the final two quarters.

The Lakers made five of 17 shots and had five turnovers in a third period in which they were outscored, 31-13. An 11-point second-quarter lead turned into a 16-point deficit by the 3-minute, 33-second mark of the fourth quarter.

Young, who has made 29 of 54 (53.7%) three-pointers over the past seven games, hit four shots from beyond the arc in the first nine minutes of the game and inexplicably didn’t take his next shot — a made three-pointer — until the 9:26-mark of the third quarter, a span of about 17 minutes.

There wasn’t enough ball movement, and the Lakers finished with just 15 assists. There was virtually no help defense in the second half, which featured a succession of unforced errors, turnovers, low-percentage shots and uncontested shots for Dallas. Even worse, the Lakers seemed to lose their will to fight.

Asked if his team was outworked during the third quarter, Walton said, “Um, I think so.” Young said the Lakers “got outside of ourselves. We weren’t looking to pass the ball. There were a lot of one-on-ones in the second half. The fans deserve a better effort, better play.”

Reserve forward Thomas Robinson, whose strong play in place of the injured Larry Nance Jr. and Tarik Black has been one of the few recent bright spots, said Walton’s post-game message resonated among the players.

“Yeah, I mean, we can’t use the excuse of us being a young team and be like, ‘OK, cool, we’re [12-24] because we’re young,’ ” Robinson said. “Forget that. We’re getting leads on teams, 20-point leads, 10-point leads. That don’t mean nothing. We’ve got to mature earlier. We’ve got to take over these games and finish them.”

mike.digiovanna@latimes.com

Twitter: @MikeDiGiovanna

Staff writer Tania Ganguli contributed to this report.