The 21-year-old singer starts off by penning a story about certain characters, but looking back at his finished lyrics, can see how they have been inspired by his own experiences and ideas.
Asked his favourite song on his album ‘Zeros’, he said: “I guess 'Be An Astronaut'. It's one of those songs I wrote two and a bit years ago now.
"It came out very, very quickly. I wrote it in 30 minutes, sat at the piano.
"A lot of the time when I'm writing songs, I'm writing a story and focusing on how the story travels, the characters and ideas, but not really putting myself anywhere in the mix.
"But after you make it, you realise that a lot of the time you are talking about yourself or something closer to you. It can feel like I'm singing to my younger self or something.”
‘Be An Astronaut’ is inspired by Declan realising how much his behaviour today is still influenced by being bullied as a child, and urges his younger self to be faithful to who he really is.
He explained in an interview: “The song has a very simple, classic, 'Do your own thing' message.
"I've realised over the past couple of years how much I was affected from being bullied in school or just how the way that people talked to you in school makes you act differently.
"I noticed that, even to this day, there are things I do or a way I will be in a situation that is totally affected by someone saying, or collectively, people saying different things to you in school, like, 'You're annoying' or 'You're getting in the way.'
"'Be An Astronaut' is the song of me maybe realising that a little bit and being like, you don't have to restrict yourself as a person because of other people because you're only carrying their insecurities. "It's not your fault that people have put you down in a certain way.
"It's a simple and classic pop message I guess, but felt very personal because it is actually something very relevant and something that everyone experiences."