A popular but limited definition of structural engineering is…
Structural Engineering is the Art of molding materials we do not wholly understand into shapes we cannot precisely analyze, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance.
This is from Dr. Brown in 1967 or Dr. Dykes in 1978 (For its history, see Jon Schmidt's "InFocus" column in the January 2009 issue of STRUCTURE, "The Definition of Structural Engineering.") This is clever and fun but only addresses uncertainty of forces and materials. What a limited understanding of what we do! This applied science portion of engineering is what they teach in school, so it is a popular definition in the classroom. Yes, we are experts in the ability to make decisions under great amounts of uncertainty, but that is only one aspect of our work. Stress and strain are necessary calculations but represent only a small fraction of all that we do; otherwise, we could be completely replaced by a computer. Those of us who do genuine engineering are never concerned about this.