The article discusses how precision engineering design can lead to optimal designs by using engineering sciences. It explains how scientific theory and practicality play a role in creating successful designs. The paper details factors needed for a complete product or system design and shows how mathematical design optimization can help achieve good designs. Various engineering design examples are provided to demonstrate the relevance of optimal design theory. The article also explores future trends in optimal design in the context of the 4th industrial revolution. It concludes that many engineering and scientific design problems can be optimized using new and advanced optimization techniques.