Tom Petty had never written a song for someone else until the sessions for 1981's Hard Promises. However, he obliged when Stevie Nicks asked, sitting down with his acoustic guitar to pen a tune with the Fleetwood Mac star's voice in mind.

Nicks had been itching for a Heartbreakers song for some time. Actually, she was more interested in joining the group herself.

“I just fell in love with his music and his band,” Nicks said in Petty: The Biography. “I would laughingly say to anyone that if I ever got to know Tom Petty and could worm my way into his good graces, if he were ever to ask me to leave Fleetwood Mac and join Tom Petty and the Heartbreakers, I’d probably do it — and that was before I even met him!”

Petty stuck to a strict "no girls in the band" policy, but he agreed to write a song for her. The result was "Insider," a tender tune that was intended for Nicks to use on her upcoming debut solo album, Bella Donna.

"When I wrote that song, I wrote it very quickly – I mean maybe in 10, 15 minutes," Petty told Melody Maker in 1981. "Aaah ... well, maybe give me another 10 minutes for the tune. I don't know. ... I just wrote it all down on paper and then I just picked up the guitar and tried to sing each line out. It took me maybe an hour to do that. It don't happen every day, fans! But the lyrics were real quick."

Petty could tell right away that it was a strong piece. "I thought it was one of my best songs to that point and I cut it there, just me and my guitar," he said in 2005's Conversations With Tom Petty. Initially, he felt the track was up Nicks' alley, but when it came time for her to begin work on the track, Petty started to get cold feet.

"She really liked the song, so we went to do the vocal and she started to sing harmony every time," Petty told Musician in 1981. "Because my track was playing in her headphones as a guide. So she said, 'Just let me sing the harmony one time.' So she did, and when it was over, I just sat there, in awe.

"She walked back in and said, 'How was it?' I said, 'It's amazing,'" Petty added. "She said, 'I can tell by the look on your face, you don't wanna give me this song. I'm giving it back to you right now.' I really thought a lot of her for that."

Petty couldn't help but feel a little guilty for taking "Insider" back, so he offered another one in its place: "Stop Draggin' My Heart Around," which appeared on Bella Donna. "She says, 'Wow! That's why I wanted you to write me a song — it's rock 'n' roll, that's what you do. 'The Insider' sounds like what I do,'" Petty said. "And I thought, how dumb of me, to think that she'd want me to write like her."

Listen to Tom Petty and Stevie Nicks' 'Insider'

Nicks' sister-in-law Lori added more backing vocals and "Insider" began to come together. Not everyone, though, was as enamored: "I didn’t particularly like it," drummer Stan Lynch tells UCR.

Lynch assumed this was going to be an acoustic track, so he figured he wouldn't be asked to contribute. "I didn’t think it would have drums – like, maybe a cross stick, a little tick tock or something. Then, they were like, 'Well, we’ve got this song.' I don’t even know why they put the drums on it. ... The record comes out and I remember that my drums were referred to in a review as the 'cymbal-pinged weirdness.' This made [Heartbreakers bandmate Mike] Campbell hysterical.

"It became almost like a tour thing that I had to hear about every fucking morning at soundcheck!" Lynch added. "I remember him going, 'Let’s get the drum sound. We gotta make sure we get that cymbal-pinged weirdness right!' You know, it just never ended. Campbell, it just put a burr out my ass. But all I could say back to him was, 'I didn’t even want to play on the fuckin’ record!' and he goes, 'I know.'"

The song swap didn't make much sense to Lynch either. "I thought as a trade-out for 'Stop Draggin’ My Heart Around,' I didn’t think it was a good bargain at all," he said. "I remember [the discussion], 'Well, we got 'Insider' and I’m going, 'Bad trade!'"

Still, "Insider" helped Petty's album in a crucial way, birthing its title: "I'm an insider / I've been burned by the fire / And I've had to live with some hard promises / I've crawled through the briars." Previous suggestions had included name checks of keyboardist Benmont Tench like Benmont's Revenge and Benmont Goes Hawaiian.

"I just kept waiting for a title to jump out at me," Petty told Rolling Stone in 1981. "It was the last minute when that tune came in, and I thought it applied to what was going on. The tunes, they're all just hard promises. I thought the word was funny – that a promise could be hard, that it might be a difficult promise. Like it was granite, you know, etched in stone – a promise you have to deal with."

"Stop Draggin' My Heart Around" wrestled with a strung out, likely ill-fated relationship, while "Insider" peeled back the layers further to reveal deeper vulnerability, regret and the harsh reality of a love that moves on.

"It's one of those things in a relationship that really is the stinger," Petty told Melody Maker. "You know, you didn't trust me, you couldn't trust me – that's the way it always come out. Trust."

Tom Petty Albums Ranked

He's a rock 'n' roll rarity: an artist who was consistent until the very end.

The Importance of Tom Petty’s ‘Wildflowers’

More From The Basin's Classic Rock