The author has spent approximately 50 years in the field of systems engineering. This Focus book provides a "looking back" at his 50-year run and the lessons he learned and would like to share with other engineers, so they can use these lessons in their day-to-day work in systems engineering and related fields. The book is written from a systems engineering perspective. It offers 50 lessons learned working for a variety of different companies, which can be used across many other engineering fields. The book will be of interested to students and engineers across many fields, as well as students and engineers working in business and management fields.