Generally speaking, restaurants are a lousy business. The failure rate is relatively high, and profit margins are relatively low.Every now and then, though, certain restaurant concepts just click with people. Chipotle Mexican Grill (CMG 0.29%) is one of those concepts. Fresh, custom-built burritos are a hit! That's why its top line is expected to grow nearly 14% this year and repeat the feat next year. Half of its recent, comparable growth stems from new store openings; the other half reflects existing-stor ...