The 35-year-old singer has been hit by criticism that it is insensitive to release an album and single with the title amid the coronavirus pandemic, but she's not worried about the negativity as she believes it is important to offer "hope" during such dark times.
She said: "If we don't have hope, it can get really, really dark, and this song is not just ignorant escapism happiness.
"Even though some people are going through that darkness, hopefully they can hear that one person made it through."
And Katy - who has spoken about her struggles with depression and anxiety - insisted the message of the record isn't to always be happy as she knows that's impossible.
She said: "It's not like, 'Be f****** happy! Let's see your smile!'
"I'm not stupid enough to think I won't ever have challenges again. Now I'm grateful that I have some tools to navigate through it."
The 'Teenage Dream' hitmaker has previously faced criticism over her early singles like 'I Kissed a Girl' and 'Ur So Gay' but she's always accepting of it.
She told The Guardian newspaper: "No one's above reproach. "If you're gonna get into this business and if you're gonna have anything to say, not everyone is gonna agree."
But Katy thinks forgiveness is just as important.
She said: "It's OK to say you weren't as evolved as a human five years ago than you are now...
"A lot of mistakes I've made in the past have been juvenile lack of education."
And the 'Roar' singer doesn't think there is often "compassion" for people in the spotlight who are trying to learn and change.
She said: "There is definitely not a whole lot of empathy or compassion towards people sometimes growing - or trying to fucking grow - in the spotlight. Because growth also means failing. And I've done a lot of falling flat on my face."
