Millennials struggle to make it past the crucial 90-day mark when starting a new job largely due to “own goals” such as lateness and absenteeism, a HR expert says.

Greg Weiss, who specializes in developing “onboarding” programs to help improve retention rates, says businesses face a growing challenge with the new generation.

According to Deloitte, millennials will make up 75 percent of the global workforce by 2025, but data shows this cohort have a much higher churn rate — and it’s costing money.

In 2015, the Australian arm of global consulting firm PwC estimated staff turnover in the first 12 months was costing Australian businesses $3.8 billion in lost productivity and $385 million in avoidable recruitment costs.

“Typically one in four people will turn over in the first three months, either voluntarily or involuntarily,” said Weiss, founder of HR firm CareerSupport365 and author of “So You Got the Job, WTF is Next?”

“One in three millennials will turn over in the first 90 days. The reasons for failing, 62 percent is poor performance, 50 percent is absence, 25 percent is lateness and 30 percent is gross misconduct.”

Weiss said absence, lateness and misconduct were “clearly an own goal,” while poor performance could be a result of the employee not knowing what was expected of them or overstating their abilities.

“The first three months of anybody’s employment are fraught with risks on both sides,” he said. “Often companies’ recruitment processes are at fault, on the employee side it may be that they didn’t understand what the company was wanting or have oversold themselves.”

Younger people are also more likely to quit voluntarily.

“Younger people will typically say, it’s not as great as I want, not as exciting, you’re underpaying, or frankly at the millennial end they’re just lazy, and I mean that genuinely,” he said.

While he didn’t want to generalize and say “every millennial is like this,” Weiss said “broadly it’s an entitled generation” and “probably also over-informed as well.”

“People are constantly on their phones, constantly wired to hear where the grass is greener,” he said.

“Every[body] is looking at everybody else’s highlight reel. People are not posting about how crap their current role is and what they’re really going through, they’re just living the high life. It gives an over-informed skew of the grass is always greener somewhere else.”

Weiss said that was compounded by a lack of “resilience” as a result of being brought up “cotton-balled and molly-coddled.”

“At the first sign of difficulty, it’s a choice of fight or flight, they typically choose flight,” he said.

Finally, young people who find themselves out of their depth are often too embarrassed to speak up. In the book, Weiss tells the story of a girl named Tory, who got a job just out of college in her early 20s.

“She realized her new line manager expected so many things out of her and she didn’t have the confidence to admit she didn’t know [how to do them],” he said.

“She felt admitting she didn’t know meant she wasn’t supposed to be in that job, so she’d get fired.”

Weiss said she would “sit in meetings like a stunned mullet.” She was eventually offered options for training but she didn’t want to be seen to be taking them for fear of being seen as incapable.

“She started to drown in stress and instead of just asking for help, she quit,” he said.

According to Weiss, nine out of 10 companies do not offer new employees “structured on-boarding” beyond basic orientation, but when they do the chance of staying on and being successful “increases by 69 percent.”

Structured on-boarding would include a sit-down with the employee to go through each of their duties one by one and explain “what good performance looks like” within the first three months.

“If there are any realistic low-hanging fruit projects that can be delivered on, then the new employee and employer should agree on those as a test,” he said.

“Sadly the majority of companies throw people in the deep end and expect them to muddle through.”