Seven years ago Arthur was made Parramatta's new NRL mentor and fresh into the job he had enough energy to keep coaching his son Jake's junior team on the weekends.

Penisini, now 19, was part of that Rhinos team that also included Sean Russell.

All three club juniors came full circle when they made their NRL debut for the Eels this season under their old coach.

"It's funny that he coached us when we were younger, it makes him kind of like a father figure," Eels centre Penisini told AAP.

"But he's also a bit more harsh on us because he knows us, he's been watching us for a while.

"He's a very honest guy and tells you straight what he thinks.

"I think it's a good thing to have as a coach and it's a good thing for me to develop my game, he's great."

Arthur has never been one to suffer fools and Penisini says he was as brutally honest with the kids as he is with his NRL players.

Many can find his upfront personality too brash, or take it the wrong way, but it's how Arthur shows he cares.

There's no filter, just honesty.

As the NRL seasons wore on and the stakes got higher, Arthur scaled back his commitment to coaching juniors because he took it so seriously.

There were times he flew back after NRL games to be with the Rhinos the next morning on next to no sleep.

That level of hard work and commitment made a huge impression on Penisini, who loves and respects the no-bull honesty from his now NRL coach and long-term mentor.

"He's very passionate for the game, he's very honest. He's not afraid to say what he thinks. He has not changed one bit," Penisini said.

"We've developed that maturity where you can have normal conversations though too.

"He'll still blow up at you if you're not doing your job properly but it's a bit more balanced.

"It's more educational around footy.

"You definitely know where you stand with Brad.

"He'll say what he thinks and then ask what you think and you'll be able to have a conversation about it.

"I love how honest he is ... he's a good coach."

Years later Penisini is four games into his NRL career and preparing for the biggest game of his life against Penrith in Saturday's sudden-death semi-final.

It comes just a week after he was awarded a controversial penalty try in the Eels' 28-20 win over Newcastle that kept their season alive for another week.

It's just one of a handful of pinch-me moments for the teenager who has always had big dreams that have been encouraged by his dad Richard.

At the start of every year the two sit down for a goal-setting session to visualise everything they want to achieve for the year ahead.

"I usually make goals with my dad, we sit down in early January and plan out some goals for the year, we write it out on a piece of paper or I type it up on my laptop and print it and leave it on top of my bed," he said.

"My dad's a very ambitious person so we do a lot of goal setting. One of my goals was to make my NRL debut.

"My dad has influenced me a lot in that, he's a big goal setter.

"He's into manifestations and talking things into existence and it's rubbed off on me.

"I'm really into that stuff, it works for me."

He also journals and sets short-term goals to achieve throughout the year and has been working on strengthening his mind with the club's mental skills coach Andrew May.

As strong as he is physically, Penisini is doing everything he can to be mentally ready to face the Panthers on Saturday.

Years of sprays from Brad Arthur can do that to a guy.

"I can't wait," he said.

"We've definitely got to aim up on our side.

"We've just got to respect (the Panthers) but also go after them as well."

Australian Associated Press