Just about every mountain-climbing movie I've ever seen includes a scene where climbers have to traverse a scary-looking chasm. Most of the time, the protagonist finds a way to cross it, but occasionally a few climbers don't make it.
Similarly, some of us come up short in funding a comfortable retirement. I surveyed a few financial planners about this issue. When working with clients, they all take into consideration work tenure, savings, investment, and spending. Most often, bridging the gap is a matter of boosting savings, curtailing spending, or both.