(von Tiesenhausen's Law of Engineering Design) If you want to have a maximum effect on the design of a new engineering system, learn to draw. Engineers always wind up designing the vehicle to look like the initial artist's concept.
(Patton's Law of Program Planning) A good plan violently executed now is better than a perfect plan next week.
(de Saint-Exupery's Law of Design) A designer knows that they have achieved perfection not when there is nothing left to add, but when there is nothing left to take away.
Any run-of-the-mill engineer can design something which is elegant. A good engineer designs systems to be efficient. A great engineer designs them to be effective.
Capabilities drive requirements, regardless of what the systems engineering textbooks say.
Any exploration program which "just happens" to include a new launch vehicle is, de facto, a launch vehicle program.
(alternate formulation) The three keys to keeping a new human space program affordable and on schedule:
1) No new launch vehicles.
2) No new launch vehicles.
3) Whatever you do, don't develop any new launch vehicles.
The ability to improve a design occurs primarily at the interfaces. This is also the prime location for screwing it up.