You don't really have to be a picky eater to fall into the trap of eating the same meals more often than you should. I can tell you from experience that working at a desk job, living alone, and generally being too busy to think about your diet can lead to easy but monotonous meals. The simplest form of nutrition is to eat a variety of different foods, but how bad can a monotonous series of meals really be? That depends on what's in the things you eat every day. Lifehacker offers a short guide to judging the nutritional value of what you eat, and tips for breaking out of the habit of eating the same thing every day.
https://en.wikipedia.org/wiki/Snail_kite