The fact that all the other Spiders believe that they became who they are only because they lost people they loved. That without grief and loss they wouldnt be heroes who save people. And Miles say "Fuck that!!!" to this idea and he's right !
Who's to say that if their loved ones had lived the Spiders wouldn't still be heroes ? Peter Parker and almost all the Spiders are good people to their core. Whether Uncle Ben died or not, they probably still would have used their powers for good ! Miles was trying to use his powers for good even before Uncle Aaron died ! Gwen was helping people before Peter died !
All the other Spiders are resigned to what they see as "fate", even Gwen who is clearly a parallel of Miles in this movie. While she accepts the narrative forced upon her and gives up, Miles refuses to do so. He has to at least TRY. It's not about having your cake and eat it too, it's about refusing to give up on the people you love, and having agency in your own life. It's about hope.
And I love this analysis from a french review of the movie ! It says :
"While most of Miles' counterparts have accepted to be "happy Sisyphus", relentlessy pushing their boulder like heroic martyrs bound to lose everything, Miles chooses to give another meaning to his life and explodes his boulder like the movie explodes the conventions of animated movies."
