It's OK, we all fall into ruts. But if you want to improve your palate, you need to increase the diversity in color, texture and flavor of the foods on your plate. Like anything you do with regularity -- drive to work, brush your teeth, run to the park and back -- eating the same foods over and over puts your mind on autopilot and dulls your ability to distinguish taste.
Trying different foods introduces new flavors and smells, which makes us pay attention, similar to taking a new route during your morning jog or on your way to work. Suddenly, you notice the scenery and the new Thai restaurant that opened up down the street.
We also learn to distinguish flavors in contrast to each other. It's often hard to tell which glass of wine has a fruitier or tangier taste without comparing it to another. You drink one, then the other, back and forth until your brain registers that one has more blueberry flavor, the other a little more citrus. It's the same thing with the food on your plate. When you take a bite of bitter Brussels sprouts, then a scoopful of sweet potato and a chunk of savory meat, your brain works harder to distinguish the differences and keep the information straight.
Give lamb a try, or contemplate that rutabaga casserole with the intrepid spirit of a dietary buccaneer. What have you got to lose?