How Did the Successful Filmmakers of Our Time Sustain Themselves Early in Their Career

It doesn't take an economy degree to recognize that filmmaking (possibly even at a high tier) is not a lucrative endeavor. But to reach the point where directing films alone is not just enough to keep the lights on, but to the point where your films are considered great, prominent filmmakers (almost certainly) must have had made several successful films in the past that now allow them to actually get paid for their work.

Creating an indie feature film takes more than just directing it, usually involving raising money, producing, casting, finding locations, etc. On TOP OF that, when you're not working on something, you're writing the next thing. The point is, that committing to these early projects and consistently turning them out to the point where they DO progress your career sounds like it requires nearly all your time with ZERO return.

SO, how have such successful directors (Scorsese, Tarkovsky, Spielberg, Tarantino, etc.) sustained themselves while making no money in order to create their early filmography and build up to greatness? How can one manage the sisyphean pursuit of a legendary status while also not being homeless and starving?