This scene in Brand New Day doesn't get talked about enough
Spider-Man thinks he recognizes himself in Frank Castle. Both alone. Both marked by loss. But Frank throws the truth right back at him: they are not the same.
Peter isolates himself by choice. He convinces himself that the people he loves would be better off without him. That's his lie.
Frank would give everything to have his people back. He didn't choose this life.
That honesty is what forges their relationship. And it's what pushes Peter, later in the film, to stop running from Peter Parker and go back to the people who love him.
Frank Castle saved Peter Parker by telling him the truth.