"Wonder" is a contemplative track where Shawn Mendes reflects on his life and contemporary society. He asks a series of rhetorical questions, and in doing so bares his psyche to the listening public.
Mendes starts off the song by imagining a world where people take a middle ground in situations rather than refusing to tolerate a view that isn't their own.
I wonder, wouldn't it be nice To live inside a world that isn't black and white?
He wonders what his pals think about their relationship now he's a successful pop star.
I wonder what it's like to be my friends Hope that they don't think I forget about them
During the loved-up chorus, Mendes ponders his feelings for his girlfriend, Camila Cabello.
Right before I close my eyes The only thing that's on my mind Been dreaming that you feel it, too I wonder what it's like to be loved by you, yeah
Speaking to Radio.com's Julia about the song, Mendes said: "I feel like 'Wonder' is in a lot of ways me just reflecting on my life, and life in general… I've never really done that before… probably because I didn't have the mental capacity and clarity to even be able to reflect, and also probably because I was really scared of what people would think if I started to reflect in my music."
During the second verse, Mendes comments on toxic masculinity.
I wonder, when I cry into my hands I'm conditioned to feel like it makes me less of a man
The lines are inspired by Mendes' relationship with Camila Cabello. He explained to Radio.com, "I thought that I was a pretty open, emotional, guy until I started being in a relationship with someone that I really, truly love and, realizing that 'oh no, I really have this big ego, and I don't want to show her that I'm hurting and I don't want to show her that that offended me, and like I want to be the man, and I want to be strong in this relationship.'"
Musically, the song features a widescreen, anthemic sound. Shawn Mendes wrote and produced the song with:
Directed by Matty Peacock (Selena Gomez's "Boyfriend"), the special effects-filled video finds Mendes standing on top a speeding train, running through a forest and emoting by the sea cliff edge as he is drenched by the rain.
Angus Young created the distinctive opening guitar part for "Thuderstruck" by playing with all the strings taped up, except the B. He learned the studio trick from his older brother George Young, who was the rhythm guitarist for The Easybeats.