We know about investors' psychology. We know how the herd can overturn a single stock in a single day, whether it is a budding IPO or an old-timer.
How about risk? How do we perceive it? Do you perceive risk the way that I do? Did I perceive it the same way that I perceived it a decade ago? Will I perceive it the same way that I do a decade hence?
Some reflection on these questions is necessary ... for inevitably, your responses will differ from mine.