By the time Robin Williams filmed Good Will Hunting, he'd already dealt with his own drug issues and been struggling with sobriety. Hell, he visited John Belushi a few hours before Belushi overdosed.^

The article doesn't mention it, but the park scene is a response to the earlier office scene.

Office scene (aka painting scene): https://m.youtube.com/watch?v=SuBx0oy__EI

Park scene: https://m.youtube.com/watch?v=8GY3sO47YYo

Full disclosure: outside of Casablanca, these two scenes are my favorite in cinema

One of the things that makes them so watchable is the little ticks that Robin Williams puts in (probably from his improv experience). Maybe he doesn't have the precise lived experience, but the man knows how to emote trauma.

In the office scene, there's a neat turn right before the painting moment where they're talking about weightlifting and Robin Williams' character gives a "Don't fuck with me, kid" warning response ("285. What do you bench?"). Of course, Matt Damon's character just zooms right past it.&

Similarly, the park scene has a great beat where after he says "You've never been out of Boston." he waits for Matt Damon to acknowledge what he said.+

^ https://web.archive.org/web/20140816025724/http://franksreel...

& Office scene, 2:03 https://m.youtube.com/watch?v=SuBx0oy__EI&t=2m3s

+ Park scene, 0:41 https://m.youtube.com/watch?v=8GY3sO47YYo&t=41s