I think the difference between a good song and a great song is... honestly, I think the lyrics, because if you have a really solid melody and solid track and everything is there but then the lyric is just okay, then you've got a good song.
I've always felt my spirit animal was a Tiger, so it's funny that now in 'Roar' with Katy Perry - which is a song we write together - there's the line: "I got the eye of the Tiger..." So I feel like there's a little bit of me in there.
There's a feeling that you get when you write songs where... it feels like it's destined to do something. Then sometimes you get that feeling with a song and it never goes anywhere, that happens all the time too, so you never really know.
I've been close friends with Katy since teenagers, before she was Katy Perry. She's always been a great resource for me to pull from and watch - from her choice of how public she wants to be about her personal life on down. I also watched her develop from the coffee-house singer-songwriter I knew to her be to playing arenas and killing it.
I got called to write for Aerosmith, nothing ever came of it, but I ended up spending the day with Steven Tyler and going to his house and we sat down at the piano, just me and him, and he sang for me and played, then he asked me to sing for him, and then we sang harmony together. That was just a big moment where it was like 'oh my god, my life is crazy!' It was really cool.
When I go and write with other artists - a lot of the time it's with them - it's like a therapy session almost. I ask them what they're listening to and what they're going through and what their influences are and I try to get inside of their head and step into their shoes for a second.