It would seem to me that at the top of the list of things that people are blind to is the long-term effects of short-term thinking, instant gratification, comfort-seeking, and conformity, especially as it applies to their health and self-worth.
That is the start of this excellent article from the Make Aging Work blog by Gary Foster.
He dives into how this affects our thoughts on aging and how being blind to certain things limits our ability to age successfully.