A surprise quarterly profit puts Carvana investors in the driver's seat.Used vehicle retailer Carvana (CVNA 2.44%) is about as cyclical as a business can get. If the economy is shaky, people will often keep driving their current vehicles rather than buy newer ones.Yet, even while America's economy struggled somewhat under high interest rates and stubborn inflation, Carvana and its shareholders had a successful 12 months. Now, its greatest triumph could be achieving profitability -- something that shouldn't ...