According to Jack in a Reddit AMA on 6/12/2017,

All My Heroes is about how the world can just disappoint you over and over and sometimes in the strangest way that gives you power to do better, especially for the ones around you who you love. Just do better the shitter things get."

On Twitter he connected this song to his previous hit “I Wanna Get Better”:

[All My Heroes] is almost like a part two to “I Wanna Get Better.” “All My Heroes,” to me, is like the adult version. It’s the “I Wanna Get Better” that you scream out in the real world when you’re on your own."