My first few apartments in New York were near the 6 Train. Using the 6 Train as your primary train is like eating from a salad bar and filling your bowl with only croutons. It may work for you, but only if you have specific, limited requirements and a tiny imagination.
It was several years before I felt comfortable with the rest of the system. If I was on the West Side and I needed to get to Yankee Stadium, I had to actually consult the map and think twice.
Now I live Uptown, work in Midtown, and have a wide variety of routes at my disposal. The labyrinth went from over-my-head to back-of-my-hand, though I can’t pinpoint the moment when the information fully settled. But it’s there now and it feels good to master something that seemed so complex at first.
As long as we’re not talking about Brooklyn and Queens. That’s just a mess.