Def Leppard were recording 1987 blockbuster “Hysteria” in Dublin when the band decided to take a break and catch a Waterboys concert.

“They had a song called ‘Whole of the Moon,’ it was great but it was their only hit,” Def Leppard guitarist Phil Collen told the Herald. “And they refused to play their hit (at the concert). I thought, ‘Well, that was weird.’ Then they kind of disappeared.”

Collen learned a few lessons that night. First, play your hits. Second, like your hits.

“If you don’t like a song, then don’t do it in the first place,” he said. “Once it gets out there it becomes public domain and it becomes part of your DNA.”

At Def Leppard’s Aug. 5 Fenway Park gig with Journey and Heart, the band will play most of its staggering 15 Top 40 hits. Def Leppard refuses to disappoint its fans, which is one reason the band had teamed with another trek with Journey (the pair packed Fenway in 2018).

Collen said the band was pitched on a Journey pairing by their late-manager in 2006. The guitarist wasn’t sure it would work. but thought it might be worth a try.

“I remember the first show as Camden, NJ, sold out with 3,000 fans outside who couldn’t get in,” he said. “It just blew the doors off the place. There were just so many hits and everyone could sing along.”

OK, so they do disappoint, but only for fans who get turned away at the stadium gates.

Collen is an absolute shredder. In 2018, he joined guitar gods Joe Satriani and John Petrucci on the G3 Tour. But in Def Leppard he’s known for sharp, tight, hooky, almost poppy twin guitar parts (first with the late-Steve Clark, now with Vivian Campbell). For all his speed and skill, he says he prefers nuance to noodling. And he uses a surprising example to illustrate his point.

“I love Miles Davis and I think ‘Kind of Blue’ is the best jazz album of all time but (Davis fusion experiment) ‘Bitches Brew,’ I can’t even listen to, I can’t get through it,” he said. “You can do anything you like, but you mustn’t (expletive) the song up. That’s the problem that a lot of people have.”

“When you’re writing the songs as well (as performing them), you don’t want something to mess your songs up,” he added. “We as a collective group understand that.”

Some nice proof of these lessons comes on 2022’s Lep album “Diamond Star Halos.” An LP largely written by Collen and singer Joe Elliott, “Diamond Star Halos” was written with all the band’s biggest inspirations in mind: Queen, Bowie, T. Rex, Mott the Hoople, and more. Most of the record is slick, tough, big rock without any messy bloat.

During their recent trek with Motley Crue, the band was doing as many as four new ones a night. Collen says that might be a bit much (remember all those Top 40 hits the band has to choose from for each tour).

“It’s a little indulgent,” he said of cramming a set with new stuff.

Def Leppard has earned the right to play at least four new songs a night. And there are at least four from its recent catalog — including new single “Just like 73” — that would fit nicely between “Photograph” and “Animal.”

But Collen is the expert. After all, he’s successfully put together setlists since that mid-’80s Waterboys show.

For tickets and detail, visit defleppard.com