Timothy B. Schmit famously joined just in time to watch the Eagles disintegrate. Ironically, things couldn't have started in a better place for the former Poco star.

He arrived with the makings of his first showcase moment with the group, an unfinished song that would become the 1980 hit "I Can't Tell You Why."

"I did bring a portion of that song, unfinished, to them back then – because I was new in the band and they wanted to introduce me on a good note, no pun intended," Schmit told Songfacts in 2016. "And I had this little piece of a tune that they really liked. It was loosely based on my own experiences."

For a moment in time, often-contentious band members rallied around the outsider. Don Henley and Glenn Frey both made key contributions, as the Eagles completed the first song on what would become 1979's The Long Run. Schmit felt like he had good reason to be optimistic.

"I think probably the friction was part of the creativity. I'm sure it was," he told NPR in 2017. "I was the guy just trying to make things okay. I did what I can to keep the peace."

Schmit established his country-rock credentials while with Poco, but by the late-'70s the Eagles had long since left those rootsy sounds behind. They wanted to push Schmit in the same direction, crafting an R&B-infused setting for his embryonic ideas.

"Timothy joined the band and the real challenge, as Don and I saw it, was to get a piece of material for him that wasn't country," Frey told Cameron Crowe in 2003. "So ... the three of us got down to work. I said, 'You could sing like Smokey Robinson. Let's not do a Richie Furay, Poco-sounding song. Let's do an R&B song.' He said, 'Sure, love to try!'"

The Detroit-bred Frey, who had deep roots in soul music, took the lead – literally. He was featured guitarist rather than Joe Walsh, who instead provided all of the song's keyboards in the studio.

"Glenn worked everything out," Schmit told Rock Cellar magazine in 2016. "We used to call him 'The Lone Arranger.' He was so good at that, so good at figuring out parts and what should lay there."

The Eagles' sweet vocal mix completed things. "Timothy came in with the title and other bits and pieces," Henley told Crowe. "Glenn and I just wanted to surround it with everything we could."

Listen to the Eagles Perform 'I Can't Tell You Why'

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As foreign as "I Can't Tell You Why" was to earlier stand-out Poco moments like "Rose of Cimarron" and "Keep on Tryin,'" the song actually recalled a youth spent around a broad variety of music.

"Even though I grew up playing folk music — and surf music, originally — I was listening to Motown and Stax on the radio, as well," Schmit told Best Classic Bands in 2017. "That music always resonated with me. I was very pleased that the song they picked to work — and the one I was going to sing — was not country-flavored, or something that went in another direction. I was really happy to go in an R&B direction. Thrilled, actually."

It quickly became clear that something magical was happening.

"I remember when it was being developed in the studio, I knew it was a great song," Schmit told Music Radar in 2011. "I was like, 'Yes! This is an amazing debut for me.' When we finally mixed it, we had a little listening party at the studio. As people were hearing it, Don turned to me and said, 'There's your first hit.' That was pretty cool."

Henley was right. Released as the third single from The Long Run, "I Can't Tell You Why" became the album's third-consecutive Top 10 Billboard smash, mirroring the No. 8 finish of its title track.

"It was all such a great ride. I just kept pinching myself," Schmit told Music Radar. "I was pretty happy they wanted to work on the song, but I probably had a few other things I showed them, too. You really don't know what's going to be a hit until it's a hit."

Then, just months after "I Can't Tell You Why" raced up the charts, Schmit's crumbling new band went on a lengthy hiatus. A fast start now long past, he wasn't featured on another Eagles song until 1994's "Love Will Keep Us Alive."

Schmit kept it all in perspective: "You get asked to be part of one of the biggest bands in the world, and the first song you record is a song you helped write and you hear it on the radio, it's good – it's great," Schmit told Vintage Rock in 2012. "I'm really, really fortunate. There's a lot of real talented people out there with much more talent than me who just don’t get these kind of chances."

Years later, it remained one of the late Frey's all-time favorite Eagles moments. He wasn't alone.

"It’s got the mood; It’s got the 'ooh baby, baby' vocal. But, again, counterpoint — with Don and I singing against the melody and the understated, brilliant guitar stylings of yours truly," Frey told Crowe, with a laugh. "It's another song that people love in our live show. Since it is a ballad, we are not playing too loud and can hear the audience. Timothy starts, and there are thousands of people singing, 'Look at us, baby ...'"

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