BOSTON -- The Boston Celtics’ 2018-19 season was chaotic from the outside, so one can only imagine what then-rookie Robert Williams thought as he watched a highly talented team underachieve and fall flat in the playoffs.

Still, Williams seemed to take everything in stride.

“I feel like it was just a great teaching step, a great learning step to know what you can improve on and know what’s to be done,” Williams told MassLive after the Celtics’ first practice on Tuesday, dodging the question like a seasoned vet. “What standards you’re held at, and what’s below standard. I feel like last season, obviously you can’t dwell on the past, but it helped me grow a lot.”

Before last season, much was made of the example Al Horford could set for Williams -- a talented big with heaps of athleticism who slid in the draft due to negative reports about his physical and work ethic.

But Williams impressed Celtics staffers by working hard throughout the year, following in Horford’s admittedly quiet footsteps.

“He was a great leader, a non-vocal leader,” Williams said. “In some cases, you’ve got to follow people that aren’t vocal in everything they do. But off the court too, Al comes up to me all the time. ... Al was a great leader.”

Williams said Horford even reached out after he agreed to a four-year deal with the Philadelphia 76ers this summer, ending his time in Boston earlier than many expected. Horford told the 20-year-old he would blossom in the NBA, and that he planned to play against Williams in many more games.

The gesture meant a lot to Williams.

“It was kind of like a respect thing,” Williams said, smiling. “It made me feel good.”

Horford’s departure might hurt the Celtics as a whole more than any of the other high-profile departures this offseason (yes, including Kyrie Irving), but for Williams, the open spot represents a major opportunity.

The Celtics have a lot of bigs and no guarantees. Enes Kanter is talented offensively, but he struggles on the other end. Daniel Theis can space the floor, but he’s not beefy enough for some of the NBA’s biggest centers. Vincent Poirier has shown flashes of potential but he’s unproven at the NBA level. Grant Williams is undersized, but he helps teams in little ways that make a big difference. Tacko Fall is just plain big.

But nobody on the Celtics’ roster has Williams’ defensive potential as a big man. Hyper athletic with long arms, Williams protects the rim at a high level, and he has excellent mobility, which could allow him to switch around the perimeter. Offensively, he can’t space the floor (Celtics assistant coach Scott Morrison outright laughed about Williams’ attempts to take jumpers in Summer League), but he’s a very good passer who can run pick-and-rolls effectively.

“Just trying to focus on setting better screens, getting my scorers open, JT, Gordon, and just being accountable to my team,” Williams said at Celtics media day, when asked what he worked on this summer.

The Celtics will need Williams to set good screens, if he hopes to replace his former mentor. But the best sign for Williams moving forward is his commitment to improvement. His rookie year taught him how much responsibility NBA players need to take for themselves in order to stick.

“How I look at it is mental,” Williams said. “It’s obviously a big step mentally -- taking care of your body, getting treatment, eating, dietitian, doing everything right. It’s mental, all of it is mental. Once you get that set up there, get things rolling, it’s a standard that you live up to. This summer, I just felt like I needed to clean up my diet a lot, sleep, get more hours of sleep and just try to keep that rolling.”

Williams said he focused hard on both diet and getting more sleep this summer, and he’s advising his young teammates to do the same. Like Horford, he’s hoping to help inspire Boston’s youth movement.

“(I have) a lot more calmness, a lot more confidence coming into the season,” Williams said. “I just knew what coaches expected from me, what coaches been drilling in me through the whole summer.

"I’ve got to prove myself to a lot of people.”