Essentially, the economic problem stems from the fact that as humans, we have unlimited wants and needs. A need is something that can be seen as being essential to survival, such as food, water, shelter and warmth. A want is something that we would like to have but which is not essential to survival - a car, the latest version of the PlayStation, all the latest gadgets on etc.
The problem is that the world and every individual in it have limited resources in relation to the wants and needs we have. We never have enough money to get what we 'want'. There are never enough resources to make sure the health service works properly. In recent times, we have heard much about the problems faced by the armed forces in conflict zones around the world 'not having the tools to get the job done'.