Metallica is known for being a dysfunctional band, which is saying a lot given the dysfunctionality of most bands. The band is globally recognized and celebrated, but it has also had to contend with tons of tension between its members over the years. Jason Newsted is a bizarre exception.
Newsted was Metallica's bassist from 1986 to 2001. He was present during the band's commercial and critical peak, and can be heard on most of the band's iconic recordings. He walked away in 2001, however, and despite never looking back, he remains on good terms with his former bandmates. It's a miracle, but it largely came down to workload.
Jason Newsted lobbied to take a year off in 2000, but Metallica forged ahead, and set up plans to record another studio album. The bassist decided he was exhausted, and didn't want to get back to work right away. He announced his decision to quit the band, citing "personal and private reasons."
Jason Newsted quit Metallica in 2001

Metallica has perhaps the most famous example of a former band member having sour grapes over an exit in Dave Mustaine. The Megadeth frontman is seemingly still bitter over the events that led to him being booted from the band in 1983. Newsted, on the other hand, is happy with his decision.
"I have never regretted leaving Metallica," he told Rolling Stone in 2009. "It was the right thing for everyone. It was the right thing to do for the camp. That's it. I've never told anyone that I wanted to go back or anything like that—not once."
The bassist was replaced by Robert Trujilo, but Metallica drummer Lars Ulrich admitted that the band underestimated Newsted during his tenure. He went as far as to claim that Newsted's exit left a huge "dent" in the band.
Is Jason Newsted still friends with Metallica?

"[It's] a little sad, because Jason's a good guy and he put a lot of effort into the band for many years, and in retrospect he was never really fully accepted into the band," Ulrich opined. "Then when he tried to go elsewhere to satisfy his creative needs, he was told — well, barked at — that he couldn't... It just sucks."
Despite parting ways, Jason Newsted remains friendly with Ulrich and guitarist Kirk Hammett. The only person he voiced any frustration toward was Metallica singer James Hetfield, who he claims discouraged him from pursuing side project Echobrain during his final years with the band. That said, it has seemingly become water under the bridge.
Newsted reunited with Metallica when the band was inducted into the Rock and Roll Hall of Fame in 2009, and he joined them onstage to perform a series of 30th anniversary concerts in 2010. These days, the bassist is fronting the band Newsted.