I absolutely agree with William Emmanuel Yu on this one. He said:
Designers conceptualize. They create a concept based on education, experience and best practices. These are called plans, blueprints or designs.
Engineers actualize. They take concepts and implement them. This involving actually building and rendering them in physical reality.
While I agree with it, I’d like to point out that the roles of both designers and engineers are equally important because designers bring ‘innovation’ to the table while engineers make that innovation ‘possible’ in reality. A lack of either of them or their respective skills would result in no genuine progress.