What ever happened to the 'three-legged stool' of retirement?

Retirement Vacation Concept, Mature Coupe Watching the Sunset

Have you ever heard of the “three-legged stool” of retirement? If you have, it was probably a while ago. 

Once considered the ideal retirement model, the three-legged stool has fallen out of favor because one of the legs – defined benefit pensions – is not as stable as it once was, and the future of Social Security is often wound up in political maneuvering in Washington, D.C. Consider the following: