Director is the most important person on a film; though I feel producer is the most important person, ever-since films' became business! Anyways, world-over a director's career graph is similar, it is very easy to direct a film these days, with digital aiding you with your directorial debut.
Point is getting that critically acclaimed film, even if it's not; a 'hit' film, numbers get producer's at your door. 90% directors' career have a similar graph. Discovery, commercial success, consolidating position with consecutive hits and then oblivion as the style goes out, of course there are exceptions like Raj Kapoor, Manmohan Desai & Yash Chopra in India; but mostly that's the case, directors' to helm biggest hits of 90's & early 2000's are sitting idle and few of their assistants have taken over as new brigade directors.
The most common reason for directors to fail is repetitive style, because once a director builds a brand, it's almost impossible to burst out of it. Critics argue that if you see a Michael Bay movie, you're going to get explosions (closer home it's Rohit Shetty). If you see JJ Abrams movie, you're going to see lens flare. If you see a Steven Spielberg movie, you're going to see a child learn self-reliance while being hurt by the world.
Almost, all directors have a definitive pattern they follow, and only those directors that are responsive to the change the audience crave for, succeed and last long. A perfect example is Raj Kapoor, after the Mera Naam Joker debacle, he came out with a very youthful & peppy, Bobby. Who would think in the wildest dreams that an almost 50-year old would helm a teeny-bopper that will be a trendsetter in Indian Cinema?
