SIM1 - don't want to get into business 101, but there are usually three reasons why people fail at aviation:
They grossly underestimate the amount of money required - you must have the money to pay up front, and to survive for at least 6 months
They try to pay as they go along - sort of related to point 1
They are pilots
With reference to the last, pilots think that they must fly, and at any cost. You can often make money by being on the ground
If you're thinking about starting an airline, the first point is very relevent when it comes to travel agents who will do anything they can not to pay you
Phil