How many times have you heard people say something like this, “I want the optimum price and quality” or “This aircraft optimizes speed and range.”

Taken by themselves, these are nonsense statements.Optimization has two parts: a figure-of-merit which you want to maximize (or minimize), and a fixed minimum (or maximum) constraint. 

Suppose you want to buy a car. You would like to optimize price and seating capacity. You cannot have the lowest price and the maximum seating capacity at the same time. You must then pick between the following two constraint statements:
1. I want the lowest price car which will carry at least 6 people.
2. I want the car with the highest seating capacity for no more than $40,000.

Remember, “the lowest price” is always zero, unless there is a constraint.

The maximum seating capacity is probably around 600 in a jumbo jet.

There can only be one objective function, but there can be many constraints.

Getting this wrong can hurt your credibility.