Always question the value to be provided by a required capability.
Very often customers state what they think is a viable solution on a problem as a requirement. The classical story on this was first told by Harry Hillaker, the designer of the F16 Falcon. His team was requested to provide an Mac 2 - 2.5 aircraft. When they asked the question why, the answer provided by the air force was to be able to escape from combat, a capability supported by agility in the design, not maximum speed.
This lesson should be brought into software development as well. By asking for the value to be provided by a feature or requirement, its possible to provide a more elegant, better and probably cheaper solution.